The object of this rescarch is to measure the kinetics of water sorption and to explore the relationship between dielectric constant and water diffusion in chemically diferent polyimide thin films. Various bankbone structure polyimides were synthesized from dianhydrides(PMDA, BPDA, 6FDA) and diamine(3,4 - ODA). For these four samples, dielectric properties as a function of time were measured as a function of time, by using a Films Dielectric Property Analyzer(FDPA) in 100% R.h., and 25 ℃. The degree of dielectric variation by absorbing water waries from 0.64 to 0.86, and the dielectric variation coefficients(D4)in films vary in the range of 1.6x10(-10)cm(2)/sec to 5.2x10(-10)cm(2)/sec. Also, degree of change in dielectric constants for the polyimide films by absorbing water is a nearly linear function of the amount of water uptake in spite of their difference of chemical structure.