Abstract: A polymethylmethacrylate enveloped pencil lead electrode was prepared on the base of pencil lead of a 1B pencil, and it was activated by scanning for 30 cycles in the potential range from -1.5 V to +2.0 V (vs.SCE) at a scanning rate of 0.1 V·s-1, in a PBS of pH 2.20. In a base solution of pH 4.8 acetate buffer, a reduction peak at the peak potential of -0.300 V (vs.SCE) given by riboflavin at this electrod was observed, with the derivative of its peak current keeping linear relationship with mass concentration of riboflavin in the range from 1.88×10-4 to 0.376 mg·L-1, and with the detection limit (3S/N) of 4.42×10-5mg·L-1. Riboflavin in vitamin B2 tablets was determined by this method, giving results in conformity to the labelled value. Test for recovery was made by standard addition method, values of recovery were found in the range from 96.5% to 111%. Value of RSD (n=5) found was 2.5%.