Abstract: The aim of this paper was to study the method for the determination of vitamin C and its content changes in different months and parts in Sonchus oleraceus L. The absorbance of extract was scanned at 190-510 nm by the ultraviolet spectrophotometer. The maximum absorption is 267 nm and the content was calculated. Results showed that the content of vitamin C in different parts was flower>leaf>stem>root in April and flower>leaf>root>stem from May to July. Vitamin C content in leaf was higher in April and in flower was higher in May. This method is simple, quick and accurate. The results were useful to the further development and utilization of S.oleraceus L. resources.