The microwave Zeeman effect of N^H_3 inversion spectra was investigated at strong magnetic field to observe molecular g-factor in the decoupled state of spin-rotation interaction. The result on J, K = 1, 1 line shows the transition from Zeeman effect to Paschen-Back effect near 10, 000 oersteds. The obtained molecular g-factors for several different JK value give some information on g-factor of N^H_3 both parallel and perpendicular to the molecular axis
