Abstract: In a process for producing a foamed polyolefin article which comprises melting and mixing a polyolefin, a volatile organic blowing agent, a cell size-controlling agent, and an ester of a long-chain fatty acid and a polyhydric alcohol in an extruder comprising a feed zone, a compression zone and a metering zone, and extruding the resultant molten gel into an area having a lower pressure than the pressure of the inside of the extruder, the improvement wherein said ester is at least one ester of a long-chain fatty acid having 8 to 20 carbon atoms and a polyhydric alcohol having 3 to 6 hydroxyl groups, and said ester is fed in the molten state into the molten gel within the metering zone and mixed with it.