Abstract: The content of vitamine B_2 (Ⅰ) in Weitaxin tablets was determined by spectrophotometry. An accurately weighed portion of the powder. equivalent to about 400 mg of Ⅰ was transfered to a 100 ml volumetric flask, 60ml of N/50 glacial acetic acid was added and heated in a water bath until the Ⅰ was dissolved, after cooling. dil. with N/50 glacial acetic acid to vol., mix, and filtered through a GS-4 sintered glass funnel. The absorbance of the resulting solution was detd. in a 1-cm cell at 420 nm, with a suitable spectrophotometer. Ⅰ is calcd. from the calibration curve prepd. The mean recovery of Ⅰ was 98.87% with a cv of 0.42%.