The deterioration of poly(ether imide)/carbon fiber thermoplastic composite due to the solvent diffusion was studied for both prepares and laminates. From the results of mass uptake determined in various solvents, nitrogen compounds and halogenated hydrocarbons were found to be effective solvents to the sorption of PEI/carbon fiber composites. Sorption kinetics for nitrobenzene, methyl benzoate and methylene chloride was considered by the mass uptake vs sorption time plots. It has been found that sorption phenomena of these solvents fur both PEI/carbon fiber prepares and laminates are two-stage non-Fickian diffusions. As the solvent temperature is increased, the rate and equilibrium mass uptake of solvents also increase. SEM micro-graphs show that the debonding occurs in the solvent diffused prepares between the matrix and carbon fiber with the progress of diffusion. The delaminating of laminates were also observed from optical micro-graphs, and this caused the decrease of flexural modulus and strength.