In order to know the depletive changes of sulfadimethoxine and oxytetracycline residues in se겨m of dairy cattle intramusculally administered with sulfadimethoxine sodium(SDS) and oxytetracycline(OTC), the concentration of sulfadimethoxine and oxyteracycline was measured in serum of dairy cattle with using high performance liquid chromatography(HPLC). SDS and OTC was intramuscularlly administrated to dairy cattle at the rate of 10mg/kg(SDS) and 10mg/kg(OTC) body weight(recommended therapeutic dose) once to four dairy cattle. There were investigated the depletive changes of the sulfadimethoxine and oxytetracycline in serum of dairy cattle at the time 2, 4, 8 hours, 1st, 2nd, 3rd, 4th and 5th day after administration SMS and OTC, respectively. The results obtained were summarized as follows; 1. After intramuscularlly administration of the SMS, the mean concentrations of sulfamethazine in serum according to the time lapsed were showed 33.964 $pm$ 4.435ppm at the 4 hours after withdrawal of medicated sulfadimethoxine sodium. And gradually according to the time lapsed, the concentrations of sulfadimethoxine residues in serum were significantly (p<.05) decreased 6.596 $pm$ 3.402 ppm at 1st day, 0.217 $pm$ 0.119 ppm at 3rd day and 0.057 $pm$ 0.032 ppm at 4th day, respectively. 2. The mean residual concentration of OTC in serum according to the time lapsed after intramuscularly administration OTC were showed 0.743 $pm$ 0.368ppm at the 8 hours. And gradually according to the time lapsed, the mean concentrations of OTC residues in serum of dairy cattle were significantly(p<.05) decreased such as 0.057 $pm$ 0.047ppm at 3rd day and 0.039 $pm$ 0.016ppm at the 5th day, respectively. In conclusion, this study could be suggested the relationship between administrated period, sulfonamides and tetracycline residual aspects in serum, and the importance of observing ceasing period of antibiotic drugs before forwarding livestocks to slaughter, Thus, this results would be able to be used the basic index for prevention of sulfonamides and tetracycline residues in dairy breedings.