OBJECTIVE: To evaluate the spermatotoxicity of gold nanoparticles. DESIGN: Experimental study. SETTING: A university in Thailand. PATIENT(S): Single-donor fresh semen sample. INTERVENTION(S): A mixture of gold nanoparticle solution and semen was prepared and further analyzed. MAIN OUTCOME MEASURE(S): Spermatozoa appearance. RESULT(S): After mixing the semen with a gold nanoparticle solution, 25% of sperm were not motile. Penetration of gold nanoparticle into the sperm heads and tails was observed. CONCLUSION(S): Spermatotoxicity of the gold nanoparticle can be detected.