A thermoplastic resin composition containing an oxygen-absorbing agent, wherein a resin matrix of the thermoplastic resin composition is substantially non-compatible and is composed of a blend of thermoplastic resins or elastomers, and the non-compatible thermoplastic resins and elastomers are present as a non-uniformly distributed structure in the resin matrix. The packaging container or cap of this invention suppresses the lowering of flavor retention incident to the dissolving out of the oxygen absorbing agent or its oxidation product even after retorting sterilization. The preservability of the contents and flavor retention can be achieved for a long period of time. According to a preferred embodiment, the oxygen absorbing speed can be increased. After storage for a long time, or after heat sterilization, a rugged state does not occur. There can be formed the oxygen-absorbing resin composition and the packaging container having excellent outer appearance.