This paper described the simultaneous determination of sulfadiazine (SD) and trimethoprim (TMP) in tablets co-Trimediazini by dual wavelength spectrophotometry multriplication subtractive method. This method was based on the measurement of both absorbance of standard solution of SD (8-14) x 10(-6)g/mL, TMP (1-2) x 10(-6)g/mL and sample solution at wavelength 242.5 nm and 228.0nm. The average recovery and RSD of SD and TMP were 100.60%, 0.33% and 98.27%, 1.58%, respectively (n=20). The method was simple, quick and results satisfactory.