The relaxation dynamics of nonlinear optical chromophores in photo-polymer composites is studied for a basic understanding of the poling mechanism. The composite films are made up of a photo-polymer containing 0.5 % by weight of 4-dimethylamino-4′-nitrostilbene. They are poled under an external dc electric field at room temperature, followed by UV curing. It is found that for such composite films both the optical retardation and the second harmonic generation (SHG) intensity clearly decay as similar stretched-exponentials in time, and their relaxation behavior is predominantly governed by the period for UV curing. It is suggested that the optical retardation involves mostly the axial order while the SHG intensity is strongly correlated to the degree of polar ordering of the chromophores.