Pneumonia kills over two million children under-age of five every year. Oral amoxicillin was recommended by WHO as the first drug of choice for treatment of non-severe pneumonia. The study aimed to determine the clinical failure rate of amoxycillin for the treatment of childhood non-severe pneumonia at Primary Health Care Centers (PHCCs). A randomized controlled multicenter-trial study was conducted in Sana’a. IMCI strategy was used to enrollments the cases where randomly allocated to receive amoxicillin or co-trimoxazole orally for five days. Multivariate logistic regression was used for identified risk factors associated with clinical failure. A total of 254 children were enrolled, of whom 128 cases were treated with amoxicillin while 126 with co-trimoxazole. The clinical failure for amoxicillin was significantly more than co-trimoxazole (30% vs 10%) p value > 0.001. the most risk factor which significantly associated to amoxicillin failure were pre-infection in the last 6 months, while abnormal CBC and literate mothers were associated with clinical failure of co-trimoxazole (p value > 0.05). The use of co-trimoxazole as an alternative to amoxicillin for the treatment of non-severe pneumonia in the PHCCs and conducting further studies to determine the appropriate antibiotic as the first line of defense are recommended.