Introduction: Understanding the immunopathogenesis of bacterial infection has led to a marked improvement in the investigational diagnosis. M. pneumoniae is a common atypical bacterium that cause community acquired pneumonia (CAP). As many diverse microorganisms cause CAP, identification of the etiological cause is essential to guide antibiotic administration. Currently, laboratory diagnosis of M. pneumoniae is unsatisfactory, pediatricians around the word invented clinical scores to help in identifying the cause of CAP. The aim of this work was to introduce Neutrophil/ lymphocyte ratio as a simple, easy and reliable method to assist in the rapid diagnosis of M. pneumonia and to reevaluate the cut off value of M. pneumoniae clinical score (The CAF score suggested by Rodríguez and colleagues). Methodology: This prospective cross sectional study included 50 children from the age of 4 to 12 years old. Cases were selected according to the CAF clinical score. All patients were subjected to full examination and laboratory evaluation including C.B.C, CRP and Chest x-ray. Oropharyngeal swabs were used to isolate M. pneumoniae and diagnosis was made by PCR. Results: There were 6 cases positive for M. pneumoniae (12%) out of 50 patient cases. ROC curve of NLR reveals a statistically significant difference between cases infected with M. pneumoniae and other non infected cases (P value= 0.01). NLR≤ 2.1 is suggestive for M. pneumoniae infection with a sensitivity of 50% and specificity of 95%. ROC curve of CAF score reveals that scores above 10 are diagnostic M. pneumoniae infection with sensitivity of 100% and specificity of 44.19%. Conclusion: NLR is a valuable addition to the diagnosis of M. pneumoniae M. pneumoniaeM. pneumoniaeM. pneumoniae M. pneumoniae M. pneumoniaeM. pneumoniae M. pneumoniae as an important cause of CAP. Also, we suggest raising the cut off value of CAF score from 5 to 10 to improve the sensitivity of the score with a mild decrease in the specificity. Using both diagnostic tools probably enhance the diagnosis of CAP caused by M. pneumoniae.