The purpose of the present study is to investigate the potential toxic effects of some malathion formulations ( malatox, malason, agrothion and nasrlathion) that have the same active ingredient on some vital biochemical components and ultrastructural changes of nuclei of liver and kidney tissues of albino rats.      Obtained data indicated that malatox and naserlathion caused significant decrease in WBCs count (-46.6 and -25.9% below normal level), while malason caused significant increase (+10.5%) after 30 days of treatment, which returned to the normal levels after 7 days of recovery, except in case of nasrlathion (-10.4%). All malathion formulations caused significant decrease in RBCs count after 30 days of treatment without recovery to the normal level at the end of experiment. The highest effect was noticed in agrothion treated rats (-38.3 %) after 7 days of recovery and malatox after 30 days of treatment. Similar effects were noticed on hemoglobin values and platelets count of treated rats without recovery to the normal levels.       Data clearly revealed that the tested malathion formulations induced significant elevation in transaminase enzymes (AST and ALT) activity after 30 days of treatment, without recovery to the normal level, except in case of ALT activities of agrothion treated rats (+2.7%). Administration of oral doses (100 mg / kg. b.w.) of tested malathion formulations didn't cause significant effects on creatinine (Cr) concentration. But in malatox treated rats there was a significant increase in Cr concentration after 30 days of treatment (+62.5 %) without returning to the normal levels at the end of experiment (+42.9%). The same trend was observed on urea concentration of the 30 days of treatment, while after 7 days for recovery, malatox, naserlathion and agrothion caused significant increase and decrease in this vital component concentration (+46.9, +28.0 and -21.9 %, respectively).                     No sharp variations were noticed between different malathion formulations in liver cells treated rats. The results so far obtained indicated histo- and cytopathological alterations by electron microscope due to the effect of compounds when compared with to the control ones. Some sections poorly differentiated hepatocellular showing marked polymorphis of the nuclei, irregularity of the chromatin and prominent nucleoli in treated rats with malatox when compared with control. Also, in treated rats with malason, agrothion and naserlathion showed the numbers of nuclei and their content in different section by many powers of vision, results show no differ significant difference and all treatment did not induce or genotoxicity.      Kidney sections of different formulations of malathion (a.i) treated animals, revealed many phases of degenerative changes when compared with those of control. Electron microscope appeared, poorly differentiated cells containing a cytoplasmic indentation or inclusion filled with brush border material and showed also, that cytoplasm is filled with prominent granular, endoplasmic reticulum containing some dense flocculam material. Also, electron micrograph appeared, poorly differentiated in nuclei and no changes in their content such as nucleolus or chromosomes (chromatid and centromere). So, form the doses applied during 30 days results conclude that all tested malathion formulations don't show any genotoxicity in treated animals.