According to computer graphics/Grid search analysis, ${eta}-keto$ carboxylic acid of nalidixic acid which has an antibacterial activity as DNA-gyrase inhibitor has been known to have got four different conformational energy values. In orders, the energy value of conformation A,B,C and D was -6.603, -4.114, -1.766 and 7.327 kcal/mol. The difference of energy value between conformation A and D was 13.9 kcal/mol. Usually conformation C was used in literature. However, it had a energy value of -1.766 kcal/mol as the result of the analysis which is about 5 kcal/mol higher than the most stable conformation A. Therefore, conformation A is expected to be more stable than conformation C.