The poling process in nonlinear optical (NLO) polymer films is studied by the second harmonic generation (SHG) and optical retardation measurements. The PMSt polymer is used as a NLO chromophore whose dipole moment is aligned transverse to the main-chain backbone. Both the optical retardation and the SHG intensity increase during poling process and decay after poling in the same fashion. The optical retardation is found to be more sensitive to the thermal fluctuations than the SHG.