The oxidation behaviour of the AB5 type intermetallic compounds CaNi5 and LaNi5 has been studied at different temperatures ranging from 100 to 800° C. The kinetic results indicate that the element A (Ca, La) is first oxidized rapidly followed by slower oxidation of nickel. X-ray diffractograms of the oxidized LaNi5 show the formation of ternary phases like LaNiO3 and La2NiO4 at temperature as low as 400° C. A comparison between the oxidation behaviour of the two compounds reveals that CaNi5 is more resistant to oxidation and decomposition than the LaNi5 system. © 1988 Chapman and Hall Ltd.