Background & Aims: Utility of antibiotics, such as third and fourth generation of cephalosporins and carbapenems, and resistance to these antibiotics in hospital acquired infections are increased. There are scientific data that support the application of Tazocin (piperacillin-tazobactam) as an empirical treatment of moderate to severe bacterial infections. In our area there is not much information available on this topic. Therefore, we decided to determine the susceptibility pattern of bacterial species isolated in patients with infection to piperacillin-tazobactam at Alzahra Hospital (a tertiary care center), Isfahan, Iran. Methods: This cross-sectional study was conducted at Alzahra Hospital (referral and educational hospital) from 2009 to 2010. 90 clinical specimens of bacterial cultures isolated from blood, urine, and respiratory tract of patients with nosocomial infections in different parts of the hospital were included in this study. Standard methods for the detection of microbiological bacterial species were used, and the antibiogram pattern of bacterial samples was performed by using E-test method. Results: Among the 90 studied specimens in this study, 73 samples were gram-negative bacteria and the remainder was gram-positive. More than 78% of gram-negative bacteria and more than 88% of grampositive bacteria, grown in cultures of patients with nosocomial infections at Alzahra Hospital, were sensitive to piperacillin-tazobactam. Conclusion: The information obtained from this research may be a guide for physicians that work in our region for the use of empiric therapy with piperacillin-tazobactam in cases of moderate to severe bacterial infections.