Klebsiella pneumoniae is a nitrogen fixing bacteria which is prevalent with pulmonary infection. Creatine is naturally produced in human body which is metabolic waste .When nitrogen content is more in the body this leads to more amino acid synthesis finally increase the level of creatinine. We selected 27 patients who were suffering from K. pneumoniae infection in the lungs as case group and 27 patients who were suffering from Pseudomonas aeruginosa infection in the lungs as control group. There was no evidence of factors which raised serum creatinine levels in these selected patients. Serum creatinine levels were estimated on the days of receiving clinical samples ( sputum/ broncho alveolar lavage fluid endotracheal aspirate) which gave positive cultures of the above mentioned microorganisms were accepted for further analysis and patients were also selected accordingly. The mean serum creatinine level of K. pneumoniae infected group was found tobe 1.176 mg/dL while creatinine level of P. aeruginosa infected group was 1.062 mg/dL. The difference between two mean values of Serum creatinine levels in the two groups was found to be highly significant at 0.001 level. Thus it may be concluded that nitrogen fixation indirectly occurs in human body with K. pneumoniae infection.