Jason said he has begun long treatment but he will still be able to perform at a high level. He announced his condition after talk with his team. He takes pills that "have proven to be very effective in controlling this cancer."
"The prognosis, and certainly the expectations of my physician, myself and my family, is that I will live a long, full and normal life," he said in a statement on the team's Web site.
Team doctor Noah Forman said the disease - chronic myelogenous leukemia - is a slow-growing cancer of the white blood cells. About 500 new cases are diagnosed each year in Canada.
Blake is in no immediate danger and shouldn't miss any playing time, according to team doctors.
"This situation will not impact my ability to live my life as I otherwise would, and will not affect my ability to perform at my highest level for the Toronto Maple Leafs," Blake said. "I'm looking forward to my first season with the Leafs and helping our club compete for the Stanley Cup."
Blake scored 40 goals last season for the New York Islanders and signed a $20 million, five-year deal with Toronto in the offseason. The four-time 20-goal scorer had 40 goals and 29 assists last year with the Islanders.
"Jason will be able to continue to play fully with the team and will be monitored closely by both the team's physician and his CML specialist," Forman said.