3, rotenone exhibited a dose-dependent toxicity. The IC50 values were found to be 50 nM at which only 50 percent of cells were viable comparining with control cells. Thus, from the above results, celastrol and rotenone were used for further experiments at a concentration of 40 µM and 50 nM respectively To study the protective effect of Celastrol against rotenoneinduced cytotoxicity, S.H. -SY5Y cells are pre-treated with 40 µM Celastrol for 90 min as described by followed by rotenone for 24 h. As illustrated in Fig. rotenone significantly decreased the cell viability, while Celastrol prevented cells from rotenone-induced injury. The present results were in par with earlier reports of .