This study evaluates the toxic effects of deltamethrin and lambda-cyhalothrin on Xenopus laevis tadpoles after 168 h of exposure. The LC50 of deltamethrin and lambda-cyhalothrin at 168 h was calculated as the mu g of active ingredient per liter (mu g AI/L). According to these values, the LC50 was 6.26 and 3.94 mu g AI/L for deltamethrin and lambda-cyhalothrin, respectively. Several enzymes were studied for early signs of intoxication following exposure to the pesticides for 24 h. Glutathione-S-transferase, carboxylesterase, and lactate dehydrogenase were inhibited by lambda-cyhalothrin, and both pesticides inhibited acid phosphatase and aspartate aminotransferase. In contrast, acetylcholinesterase was activated by deltamethrin. The results suggest that X. laevis is sensitive to the pyrethroids that were tested, and the enzyme responses suggest that they are potential biomarkers for evaluating the toxic effect of pyrethroids on amphibians in environmental conditions.