A total of 150 clinical samples were collected from different hospital in Baghdad. Morphological & biochemical characterization showed that 71 isolates (47.3%) were Staphylococcus aureus. The rapid iodometric method was used for the detection of (3-lactamase production which showed that sixty out of seventy one S.aureus (84.5%) were P-lactamase producers. Twenty nine isolates (40.8%) were regarded as rapid producers due to their ability to decolorizing the the blue color of iodine- starch complex within few seconds. All S.aureus rapid p-lactamase producing isolates were resistant to penicillin G , ampicillin, carbenicillin & cephalexin. 90%resistant to amoxicillin.80% resistant to cloxicillin, cefuroxime & ceftazidime. While all were sensitive to cefotaxime & rifampin. Determination of minimal inhibitory concentrations of some |3- lactam antibiotics (penicillin G ,ampicillin, amoxicillin, carbenicillin, ceftazidime, & cefuroxime) showed that thetested S.aureus rapid p-lactamase were able to grow on high concentration (500fig/ml) of different tested p-lactam antibiotics. While S.aureus non P-lactamase producing isolates showed only slight resistance to penicillin & ampicillin (25 fig/ml) & were sensitive to the other tested P-lactam antibiotics (amoxicillin, carbenicillin, ceftazidime & cefuroxime). Results from agarose gel electrophoresis revealed that all S.aureus rapid p-lactamase producing isolates have a large plasmid & which was absent in non P-lactamase producing isolates . The plasmidless cells obtained from treatment of S.aureus rapid P-lactamase producing isolates with ethidium bromide were rendered sensitive to all P-lactam antibiotics & were unable to decolorize the blue color of iodine- starch complex. This result indicated that genes responsible for resistance to P-lactam antibiotics & hence to p-lactamase production are carried on this large plasmid. Results from transformation experiments1 showed that this plasmid was capable to show its expression in Gram-negative bacteria, E.coli MM 294 transformants were capable of decolorizing the blue color of iodine-starch complex & were rendered resistant towards tested p-lactam antibiotics.