Objective To investigate the proportion of streptococus pneumonia(SP), haemophilus influenzae (Hi),branhamella catarrhalis (BC), chlamydia pneumonia (CP) and mycoplasma pneumonia (MP) in children with acute pneumonia.Methods Fifty-three hospital-treated children with acute pneumofmonia were included in a prospective study. The enzyme immunoassay was used to detect antibodies in paired sera against non-capsulated Hi, Hi type-B capsular polysaccharide and whole cell, antibodies against pneumococcal pneumolysin, C-polysaccharide and pneumococcal pneumolysin, C-polysaccharide, surface protein A in circulating immune complexes and antibodies against BC and MP. Antibodies against CP by immunofluorescence in paired sera as well as blood cultures were detected in these cases.Results The evidence of bacteria infection was demonstrated in 32 cases (60.4 %) among children with acute pneumonia, of which 11 cases had 2 or 3 organisms coinfection. In these causative agents,SP and CP were the most common organisms (11/53 cases respectively,20.8 %), followed by MP (7/42,16.7 %),Hi(7/53,13.2 %).Conclusion SP,Hi,CP and MP are common causative agents of children with acute pneumonia and multi-agents coinfection isn′t ingnored in our empiric antibiotic therapy for the disease.