This thesis is an attempt to study the nonlinear optical(NLO) properties of different nanoparticles (NPs)for optical limiting, optical switching, and fluorescence applications. NLO properties of three different types of NPs are studied. These NPs show typical NLO properties due to their different energy level systems. Semiconductor NPs: Bandgap energy between the valance and conduction bands is responsible for all optical properties in semiconductor NPs. Bandgap of these NPs is tuned by changing the size. The size dependent multi-photon absorption of these NPs were studied. Metal NPs: Surface plasmon resonance band absorption plays key role in optical properties of metal NPs. Tuning surface plasmon resonance band, we have observed interesting changes in NLO properties of these NPs. Phthalocyanine NPs: Optical properties of these NPs depend on the high energy B (Soret) band and the low energy Q band(s). These NPs exhibit an increase and a blue shift in the B-band, and quenching of the Q-band compared to ordinary phthalocyanines molecules. Due to quenching of the Q-band and enhanced B-band, these NPs show NLO behaviors similar to semiconductor NPs.