p-nitrotoluene is an important organic intermediate widely used in pesticide, foamed plastics, dyestuff and medicine industries. In this paper, Crusian carps (Carassius auratus) were exposed to dilute p-nitrotoluene solutions with different concentrations of 0, 20, 40, 80, 120, 160, 240 and 320 μg/L; the subsequent physiological responses to the chemical were observed, and the variation characteristics of blood corpuscles, ovaries and oocytes were studied by bio-microscopy. Results showed that even very low concentrations of p-nitrotoluene would lead to toxicosis and even the death of Carassius auratus. The bio-microscopic structures revealed that, compared with the compartment of Carassius auratus growing in the p-nitrotoluene-free water (the control group), the lower concentrations of p-nitrotoluene (for example no more than 80 μg/L) would result in the faster disintegration of erythrocytes and the significant enlargement of oocytes, while the higher contents of p-nitrotoluene (no less than 240 μg/L in this case) would inhibit the division of cells and their further growth, even degenerate blood corpuscles and ovaries, suggesting stronger estrogenic activities.