This paper reports the dynamics of the photochromic reaction of crystalline N-(3,5di-tert-butylsalicyliden)-4-aminopyridine which can be applied for nonlinear optical photoswitches. The transient absorption spectra of the microcrystalline powder were measured by femtosecond diffuse reflectance spectroscopy and compared with those in ethanol solution. Similar photochromic reaction occurs in solid state and in solution, however some intermediate species were observed before the long lived photoproduct in solid state probably due to steric hindrance in the crystalline state.