The three plasmid borne alternative dihydropteroate synthetase (DHPS) genes namely sul1, sul2 and sul3 genes were heterologous in amino acid sequence and have about 40 – 50% identity. However, they have same DHPS activity with disc diffusion zone size of 6 mm with suphamethoxazole disc in our previous study. Sul1, sul2 and sul3 genes were observed in sulphamethoxazole resistant uropathogenic Escherichia coli (UPEC). In this study, all the three genes were cloned into E. coli host and minimum inhibitory concentration (MIC) was investigated for each sul gene to compare the activities of sul genes. The MIC values of E.coli containing sul2, sul1 and sul3 genes inserted recombinant plasmid were observed to have 18.5 mg/ml, 18 mg/ml and 17.5 mg/ml respectively as mean value of five experimental results. Although comparable MICs were obtained as a result, the MIC value was highest in E. coli carrying sul2 gene indicating that this DHPS enzyme activity of sul2 was strongest among three sul genes.