Ketol-acid reductoisomerase (KARI) is a promising target for the design of drugs and herbicides yet there are only few reports on the molecular design of KARI inhibitors. Ketol-acid reductoisomerase(KARI) of S. aureus was isolated but its protein is not having any predicted 3-Dimentional structure available in PDB (Protein databank) as elucidated by X-ray crystallography or NMR. Its structure was determined in silico by sequence homology. The gene sequence of the KARI of S. aureus was known and its protein sequence was subjected to PSI-BLAST at NCBI. There was neither identical sequence available nor the nearest neighbour in the blast analysis. Then an alternative method for finding the homologous protein i.e., fold prediction method was used.  The generated model was subjected to several repeated cycles of energy minimization using SPDBV software and the final model was subjected to stereo chemical evaluation. The homology modeled structure of the KARI of S. aureus was docked by different inhibitors by Molegro virtual docker and the data were presented.