A sacrificial brazing fin stock for use in an aluminum base alloy heat exchanger comprises an aluminum base alloy core having a grain size of 100 .mu.m or more and consisting essentially of 0.5 to 2 wt. % manganese plus iron, said manganese being more than iron, 0.1 to 0.7 wt. % zinc, 0.001 to less than 0.02 wt. % tin, and balance aluminum and a cladding consisting of one material selected from an Al-Si base alloy and an Al-Si-Mg base alloy.The above fin stock protected a main tube of the heat exchanger from a pitting corrosion and led to a greatly expanded use of the aluminum base alloy heat exchanger.