In recent years, silicon dioxide (SiO2) nanoparticles (NPs) have widely used in industry, personal care products, cosmetics, construction, catalysis, dyes (pigments) and pharmaceutical applications. This use of nano-SiO2 has been associated with environmental toxicity concerns. Therefore, the aim of this study was to evaluate the effect of SiO2 NPs on the motility parameters of Oncorhynchus mykiss spermatozoon. Afterwards, Sperm samples were incubated with different concentrations of SiO(2)NPs (1, 10, 25, 50 and 100 mg/L) at 4 degrees C for 3 h. According to the obtained results, there were statistically significant (p < 0.05) differences in VSL (m/s), VAP (mu m/s), BCF (Hz) and MAD (degrees) values, while there was no significant difference (p > 0.05) in VCL (mu m/s), LIN (%) and ALH (mu m) values in spermatozoon motility against SiO2 NPs exposures at different concentrations. As a result, especially 100 mg/L concentration of SiO2 NPs has negative effects on rainbow trout (Oncorhynchus mykiss) spermatozoon in terms of sperm motility.