There is disclosed herein an oxygen absorbent composition comprising an organic oxygen absorbent (A) which neither absorbs nor releases moisture and in which an oxidizable main component is supported on a porous silicate having an average pore diameter of 200 to 5,000 .ANG., and a formaldehyde absorbent (B) which neither absorbs nor releases moisture and is at least one of an amine, a thiol and a sulfonic acid that is supported on a porous carrier. According to this invention cultural assets made of organic materials which are required to be kept in a medial humidity atmosphere can be preserved in an atmosphere of a medial humidity, a low oxygen concentration and a low formaldehyde concentration by the use of the disclosed oxygen absorbent composition.