In this paper are reported the effects on the swelling and the diffusion properties of nylon 6 and polyethylene terephthalate (PET) film in 32 organic solvents differing widely in chemical characteristics.The degrees of swelling are correlated with the solubility parameter δ of the solvent. It was observed that maximum swelling take place with solvents whose solubility parameter approaches that of PET δ=10.7 and that of nylon 6 δ=13.6. However the swelling of PET are closely connected with the dispersion component of the solubility parameter δd, and maximum swelling of PET take place with solvents at δd= 8.3.The rate of diffusion are correlated with the degree of swelling. The diffusion coefficients of C.I.Disperse Red 17 increase with increasing the degree of swelling of polymers by solvents, but the slope of the lines are different by combination of polymers and solvents.