Microbial, plant and studies in aquatic animals have shown that landfill leachate is toxic. However, more information about its effects in terrestrial animals is required. As a part of ongoing research into the toxic effects of landfill leachate in Nigeria, we evaluated the acute effects of raw and simulated leachates from Abadina, Orita-Aperin and Oworonsoki dump sites, all in Southwest Nigeria, in mice. Raw leachates were obtained directly from the dumps while the simulated leachates were obtained from the solid wastes in the laboratory by using the ASTM method. The samples were designated Abadina raw leachate (ARL), Orita-Aperin raw leachate (OARL) and Oworonsoki raw leachate (OWRL); and Abadina simulated leachate (ASL), Orita-Aperin simulated leachate (OASL) and Oworonsoki simulated leachate (OWSL). Their physico-chemical properties were determined in accordance with standard analytical methods. Young male mice (12-15 wk) weighing 24-31 g were exposed to 1%, 5%, 10%, 25%, 50% and 100% concentrations of each test samples for 5 consecutive days and were observed for a period of 96 h for toxic response. Mortality recorded at different times for each sample at the various concentrations was mostly within the last 48 h of the exposure period. The LC50 obtained are 100% for both ARL and OARL, and 50% for OWRL; and 83.50% and 50% for ASL and OWSL, respectively. It was indeterminate for OASL. Apart from this, other toxic effects like weight loss, sluggishness, loss of hair and reduced food intake were observed. The investigated samples were ranked as OWRL > OWSL > ASL > OARL > ARL > OASL. The observed effects were due to the toxic constituents present in the leachate samples. This suggests that the mixtures have the potential to cause harmful effect to public health and our environment through seepage into ground or surface water.