The Gates Foundation has withdrawn a $5.2 million grant to a Canadian research center for planned tobacco control work in Africa, after learning that the chairwoman of the center’s board was also a board member for a unit of one of the world’s largest tobacco companies.

Officials said antitobacco activists discovered last month that the executive, Barbara J. McDougall, who has headed the board of governors at the Canadian International Development Research Center since 2007, has also been serving since 2004 on the board of Imperial Tobacco Canada, a subsidiary of British American Tobacco.

The tobacco company affiliation, listed on Ms. McDougall’s law firm biography, had not been included on news releases about her appointment to the research center, which reports to Canada’s parliament and provides financing for tobacco control and other work. Apparently, tobacco industry opponents had not made the connection until recently.

“We are deeply disappointed by this revelation and feel this conflict is unacceptable as we work to support meaningful tobacco control programs in Africa,” Kate Teela, a program officer with the Bill and Melinda Gates Foundation, wrote in an e-mail message to African alliance members last weekend.

Antitobacco activists said the action came after the African Tobacco Control Alliance threatened to withdraw from a planned meeting of tobacco experts throughout Africa in Senegal next week. The Canadian research center was to be a co-host of the meeting, paying its share of the costs from the Gates Foundation grant. Without that money, the meeting’s status was unclear Monday.

The Gates Foundation, which is based in Seattle, finances many international health and antitobacco programs. It withdrew its grant to the Canadian center on Friday, but the action was not made public until Monday through news releases by the foundation and other groups.

The Canadian research center said in a statement Monday that it “understands and respects” the grant’s withdrawal but was disappointed. The statement, from a spokeswoman, Angela Prokopiak, said the center would continue working on tobacco control in other ways and was still receiving Gates funds for other ventures. Ms. McDougall, a former member of parliament, did not return telephone and e-mail messages seeking comment Monday. She currently works for a Toronto law firm.

Rachel Kitonyo, chairwoman of the African Tobacco Control Alliance, praised the Gates Foundation.

“This is clear conflict of interest and we find it deplorable,” she said in a statement Monday. Ms. Kitonyo said the African alliance was concerned with interference from the tobacco industry as it “seeks to avoid, delay, dilute and defeat laws and policies designed to reduce tobacco use.”

Imperial is the largest tobacco company in Canada. Its owner, British American, had worldwide sales last year of $21.8 billion and profits of $6.3 billion. Its revenue and profit in a region combining Africa and the Middle East were about 15 percent of its total but grew faster than in any other region last year, a company report showed.

Gigi Kellett, a spokeswoman for Corporate Accountability International, a nonprofit corporate watchdog group based in Boston, said the dual roles violated a global tobacco treaty signed by Canada and about 160 other countries.

The treaty, endorsed by the World Health Organization, cites an “irreconcilable conflict” between tobacco and health interests. A treaty guideline says signatories “should not allow any person employed by the tobacco industry or any entity working to further its interests to be a member of any government body, committee or advisory group that sets or implements tobacco control or public health policy.”

In the United States, the treaty was signed by President Bush in 2004 but was not sent to the Senate for ratification. President Obama has said he would push for its ratification but has set no date to send it to the Senate.

If that occurs, the recently established Center for Tobacco Products, part of the Food and Drug Administration, may run afoul of the industry conflict section of the treaty. Three tobacco industry representatives sit as nonvoting members on a 12-member scientific advisory committee to the F.D.A.