Inelastic longitudinal electron scattering form factors have been calculated for the 1/2+, 2.532 MeV tate in 39K . Model space wave functions, defined by the orbits 1d5/2 - 2s-1/2 - 1d3/2 can not give reasonable results for both the gamma decay transition probabilities and the form factors . The model space wave functions for 39K nucleus corresponds to the extreme single-hole wave function. Core - polarization effects are included using different models for the transition density which give reasonable agreements between the measured and calculated form factors for all values of momentum transfer considered in this work . Tassie model and Bohr-Mottelson model give better results from the valence model for momentum transfer values greater than 2 fm1 . The calculated form factors with transition density derived from the ground state density according to the shell model calculations agree very well with that derived from the empirical ground state density.