1．The effect of some transition metal salts upon the rate of oxygen—absorption by cis．polybutadiene has been studied；the salts used were acetylacetonates of Co++，Cu++，Fe+++．Mn++ and Ni++．The results show that the relative catalytic activities of these compounds depend on their cationic redox potential in the order： Co++>Mn++>Fe+++>Cu++ and Ni++．It was also found that as the concentration of the salts is in-creased．the initial rate of oxygen-absorption is also increased，while the maximum rate is only accelerated by Co++．but inhibited by Cu++ and nearly unaffected by Fe+++ and Ni++．2．Comparison has been made between the effects of bivalent cobalt salts：cobalt halides，stearate，and acetylacetonate，upon the oxygen—absorption rate． It was shown that the relative catalytic activities of different halides are similar to each other．but are slightly less active than the tWO organic salts．The effect of cobalt acetylacetonate on the maximum rate is slightly greater than that of cobalt stearate． Furthermore．it was also found that the maximum rate of oxygen-absorption is proportional to the square root of the concentration of these cobalt salts within the temperature range from 60°to 80℃． The apparent activation energy of the initial stage was found to be decreased by cobalt salts from 20 kcal／mole for the raw polymer to 16 kcal／mole：but that of the maximum rate was not affected，the value of which was 14 kcal／mole．3．The effects of four binary mixtures，acetylacetonates of Co++——Fe+++，Co++一Cu++，Co++——Ni++。and Fe+++—Cu++，on the rate of oxygen．absorption have also been inves．tigated．It was found that with the exception of the Co++—Ni++ system．all the rest showed that the more active component was inhibited by the less active one．Meanwhile，the inhibition effect depended markedly upon the molar ratio of the two components in two different ways，one with an optimum value and the other with a limiting value．Moreover，as the molar ratio was increased to 1：1 0，the effect of the Co++—Fe+++ sys—tem was synergistic，i．e．the value being greater than additive．