Two trials of external quality assessment for clinical microbiology laboratory were performed in 2004. A total of 12 specimens were distributed. Six specimens were distributed to 293 laboratorips with 277 returns in Trial I and six specimens to 293 laboratories with 274 returns in Trial ll. The acceptable percentages of Gram-stain on Streptococcus pneumoniae, Escherichia coli, Pseudomonas aeruginosa, and Enterococcus faecalis we re 96.0%, 98.5%, 97.4% and 98.2%, respectively. The acceptable percentages of bacterial identification on Streptococcus pneumoniae, Escherichia coli, Enterococcus faecalis, Staphylococcus saprophyticus, Shigella flexneri, Gemella spp.. Pseudomonas aeruginosa, Enterococcus faecalis (Trial Il), Streptococcus agalactiae, Listeria monocytogenes. Eiysipelothrix rhusiopathiae, and Eikenella corrodens were 97.5% (including 33.7% of no growth), 99.6%, 93.2%, 82.3%, 95.4% 50.7%, 98.4%, 92.3% 87.0%, 78.9%, 92.5% (including 53.4% of no growth), respectively. The acceptable percentages for antimicrobial susceptibility tests on Escherichia coli and Pseudomonas aeruginosa were relatively high, but those on Streptococcus pneumoniae and Enterococcus faecalis were not high. In conclusion, the acceptable percentages of bacterial stain and identification were relatively good. However, it is necessary that the quality assurance of the individual laboratories should be improved for antimicrobial susceptibility tests on Streptococcus pneumoniae and Enterococcus faecalis, and the selection of the most appropriate antimicrobial agents to test should be also considered.