To investigate the effects of pyrroloquinoline quinone (PQQ) (2,7,9 - tricarboxyl - 1 H- pyrrolo [2,3 -f ] quinoline - 4,5 dione) in mouse kidney, liver and testes, mice were divided into 3 groups as control, Na HCO3 and PQQ groups. 11.5 mg/ kg sodium bicarbonate and 11.5 mg/ kg PQQ were injected for 4 days to Na HCO3 and PQQ groups mice. Accordingto our morphological observations, there were no serious alterations which revealed a toxic effect of PQQ on kidney, liver and testes. Also, ultrastructrual features of glomeruli and proximal tubbules in kidney tissue demonstrated that PQQ was not a toxic agent. Keywords : Pyrroloquinoline quinone, liver, kidney, testes