Conjugation is a major mechanism of DNA transfer among bacteria which takes place in both laboratory and natural environment and brings about new characteristics. Extrachromosomal DNA called plasmid are important elements in this exchange. Resistance plasmid confer resistance to many antibiotics and in this group, penicillinase plasmid is responsible for resistance to penicillins and cephalosprins. In this study, 300 E.coli strains which had been isolated from urinary tract infections were tested by a rapid acidometric method for the presence of penicillinase, of which 95% showed to be positive. 40 penicillinase producing strain were later subjected to artificial conjunction and 25% of them transferred this plasmid to recipient bacteria. The results indicate high potential for this kind of antibiotic resistance and it’s transfer.