Using a time of flight (TOF) mass spectrometer, we obtained the multiphoton ionization (MPI) spectra of ethylamine (EA) and dimethylamine (DMA) molecules in the region of 440 nm-470 nm with a dye laser and at 532 nm with a Nd:YAG laser respectively. Both kinds of molecular ions are formed through resonance enhanced multiphoton ionization (REMPI) via Rydberg states. The fragment ions come from the dissociation of the corresponding molecular ion. The MPI-MS patterns of the two isomers are readily distinguished. The β-cleavage of the EA molecular ion is dominant. The currents of the molecular ion and the ion created by its pseudo-β cleavage are strongest in the MPI-MS of the DMA molecule. Softer ionization occurs at longer wavelengths as the initially formed molecular ions have less excess energy. The reactions of CH 4 N + ions from different precursors are also structure related: they fragment more extensively in MPI of DMA molecules than in that of EA molecules.