A method for quantitative determination of myricitrin in common myrtle (Myrtus communis L.) leaves using high-performance liquid chromatograph (HPLC) was developed. The content of the dominant flavonoid myricitrin (myricetin 3-O-α-L-rhamnopyranoside) in common myrtle leaves varied from 0.98 ± 0.02% to 1.51 ± 0.07%. The error of a single determination and the average error of the myricitrin content determination in common myrtle leaves were ±15.81% and ±4.77%, respectively, with confidence probability 95%.