The study aims to investigate the efficacy of piroline and other antibiotics in the treatment of bovine mastitis caused by Streptococcus uberis and Escherichia coli during dry-milk period. A total of 1880 cows in dry-milk period were divided into 4 groups and treated with penicillin G, ammonia benzyl penicillin, ceftiofur and piroline, respectively. The efficac for mastitis caused by E. coli were 31.2% for penicillin G, 36.9% for ammonia benzyl penicillin, 61.3% for ceftiofur, and 64.4% for piroline. For mastitis caused by S. uberis, the efficacies are 90% for ceftiofur and 94.4% for piroline. The results indicated that piroline was more effective than the other three in treating the disease. The post-treatment analysis on milk samples demonstrated absence of piroline residue Hence, piroline could be used as therapeutic agent in treating mastitis.