The black climbing rat, Rattus rattus, is considered one of the rat species that spread in different Egyptian environments. It has great importance in reducing the economic value of food and transmitting diseases. The toxicity of four insecticides (Chlorzan 48% EC, Hachi Hachi 15% EC, Nasr Lathion/Kemenova 57% EC, and Grab 2.5% EC) was tested at three different concentrations (2.5, 5 and 10%) on changes in body weight, mortality rates, and the effect on each of liver and kidney functions. As well as some histological studies in R. rattus males. Results showed that Chlorzan 48% recorded the highest effect during the various studies, as the percentage of weekly body weight gain was the lowest (5.68 gm) after one-month post-treatment. The same insecticide also caused the highest rates of mortality, reaching 40% at a concentration of 10%; on the other hand, ALT, AST, ALP and urea rates were significantly increased, while the creatinine level significantly decreased. Nasr Lathion/Cheminova 57% came in second place in terms of its effect on R. rattus individuals. The toxicity of the two previous insecticides was tested at a 5% concentration on histological changes in the stomach, liver, heart and kidneys of R. rattus; there were clear histological changes in the tissue sections examined as a result of treatment with these two pesticides.