Abstract: A method of determining thebaine in red poppy with solid-phase extraction-high performance liquid chromatography was developed. There is a good linear relationship within the range of 0.01~0.09 g/L. The correlation coefficient for the thebaine was greater than 0.999 2. The average rate of recovery for the reference substance was 100.08% and the relative standard deviation was 0.48%. The results showed that the proposed method was simple, rapid and accurate. The method has been applied to the determination of the thebaine in red poppy.