This study has the aim of verifying the morphologic alterations in the hepatic tissue of Rhamdia quelen juveniles when exposed to 0.01 mL/L of Folidol 600. Techniques of light microscopy and transmission electronic microscopy were used. The liver was target for the Folidol 600 action after 4h of contamination. Loss of cellular contour, picnotic nucleus and decharacterization of the endothelium and of the rough endoplasmic reticulum were observed. Focuses of necrosis increased significantly when compared to the control sample at the exposure times of 48 and 72 h to the organophosphate. The density of hepatocytes increased significantly in every experimental time when compared to the control sample. The number of hepatocytes with biliary pigment increased significantly in the first 72 h of exposure when compared to the control. Folidol 600 was responsible for serious alterations in the hepatic tissue of the Rhamdia quelen.