Abstract: It is an object of the present invention to provide a volatile foaming agent composition for thermoplastic resins capable of producing a thermoplastic resin foam without any shinkage or expansion after foaming.A volatile foaming agent composition for thermoplastic resins according to the present invention comprises 1,1,1,2-tetrafluoro-ethane.As the permeability of 1,1,1,2-tetrafluoro-ethane in thermoplastic resins is smaller than that of the air, volatile foaming agent composition containing 1,1,1,2-tetrafluoro-ethane and other kind of volatile foaming agent having permeability higher than that of the air can be regulated to have the permeability similar to that of the air.Accordingly, the permeating speed of volatile foaming agent from the inside of foam cells to the outside and the permeating speed of substituting air into the foam cells from outside can be balanced and any shrinkage or expansion after foaming can be avoided.