Diazinon is widely consumed for plague control in the agricultural farms and in domestic and aquaculture aspects. The present research purposed to evaluate the effect of half-lethal concentration (LC50) of diazinon on some biochemical and hematological parameters of silver carp, hypophthalmichthys molitrix, after 0, 24, 48 and 96 h. The results showed that the values of leukocytes (WBC), haematocrit (Ht), hemoglobin (Hb), MCHC, lymphocyte, cortisol and glucose were significantly increased (P < 0.05). The mount of MCV and MCH were significantly increased at 48 h and then decreased at 96 h (P < 0.05). Moreover, there was a significant increasing in neutrophils count at 48 h, and then a significant decreasing at 96 h (P < 0.05). There were no significant differences in RBC, monocyte and eosinophile counts among treatment groups at different sampling intervals. Thereupon, low-term (96 h) exposure to diazinon at half-lethal concentration (LC50) caused biochemical and hematological changes in silver carp, and offers a simply implement to appraise toxicity-derivatived changes.