Novel nonlinear optical (NLO) network polyurethane of lysine triisocyanate (LTI) with 4-[N- (2-hydroxyethyl)-N-methylamino]-3’-(hydroxymethyl)azobenzene (AZODIOL) dye as a NLO-phore has been prepared for second harmonic generation (SHG). A soluble prepolymer of LTI with AZODIOL was prepared, and then a thin prepolymer film was spun-cast on an indium tin oxide coated glass substrate. Two types of poling were carried out. One-step poling process : while high voltage between 5.0 and 8.0 kV was applied to the corona wire, the sample film was heated up and held at a temperature range of 70-190 degrees C for 10 min and then cooled down to room temperature for 40 min. Two-step poling process : while high voltage was applied to the corona wire, the sample was heated up and held at 90 degrees C for 1 h and then heated up again and held at a temperature range of 90-190 degrees C for 30 min. Then the sample was cooled down to room temperature while applying the poling field. The effects of the above poling condition and storage time and thermal annealing on SHG activity are investigated in connection with polymer structure. Better long-term thermal stability of SHG at room temperature can be obtained for the sample prepared by a two-step poling process. This better thermal stability is interpreted to be due to the smaller free volume for that sample.