Background and Aims: A new sensitive and selective method for the determination of sultamicillin in bulk and pharmaceutical preparations has been developed. Methods: The developed method is based on the derivatization of sultamicillin with 4-chloro-7-nitrobenzofurazan in pH 9.0 borate buffer at 70ºC for 60 min. The derivative was measured spectrophotometrically at 432 nm after extraction with chloroform. Results: The method was validated by linearity, LOD, LOQ, accuracy, precision and recovery parameters. The linear range for sultamicillin was 10-50 µg.mL-1 with a correlation coefficient of 0.9999. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 1.47 and 4.41 µg/mL-1 , respectively. Conclusion: The suggested method was validated, and can be applied for routine sultamicillin analysis in dosage formsfor industrial analysis.