Femtosecond near-infrared laser microscope was developed with a home-built cavity-dumped chromium: forsterite laser as a light source centered at 1.26 μm. Optimization of the pulse duration achieved 35 fs fwhm at the sample position of the microscope after passing through a 100 × objective. This system was applied to the detection of multiphoton fluorescence of some organic microcrystals. Excitation intensity dependence and the interferometric autocorrelation detection of the fluorescence clearly demonstrated that simultaneous three- and four-photon absorption processes are responsible for the production of the excited state for perylene and anthracene microcrystals, respectively. The spatial resolution along the optical axis and its dependence on the order of the multiphoton process were also discussed.