The widespread use of pesticides in veterinary medicine, agriculture, public health, and aquatic environments has increasingly threatened aquatic life in recent years. This study aimed to evaluate the acute toxicity, behavioral changes, and histological alterations caused by pymetrozine (PY) in the Nile tilapia (Oreochromis niloticus). The 96-hour LC50 value for PY was found to be 0.28g/ L, indicating the concentration at which half of the test population succumbed within 96 hours. Behavioral changes such as hyperexcitation, irregular swimming, dark coloration, loss of balance, and lethargy were observed and varied with the concentration of PY. The study also demonstrated that the mortality rate, clinical lesions, behavioral changes, and histological alterations in the gills, liver, and kidneys were all influenced by both the dosage of PY and the duration of exposure, highlighting the toxicological impact of PY on the Nile tilapia.