Abstract: Brown colored compound was formed between the antibiotics roxithromycin (or midecamycin) and dil.H2SO4,with absorption maxima at the wavelength 482 nm,and molar absorptivity (ε) of 5.00×103L·mol-1·cm-1 for roxithromycin (1.02×104L·mol-1·cm-1 for midecamycin).Linear relationship between values of absorbance and concentration of the antibiotics was obtained in the range within 17.0 mg·L-1 for roxithromycin (in the range within 20.5 mg·L-1 for midecamycin).Based on these facts,a photometric method for determination of the antibiotics was proposed,and its feasibility was proved by analyzing substantial drug tablets.