A new method for the quantitative determination of fucosterol in the marine algae Pelvetia siliquosa by gas chromatography was established. A HP-1 column programmed as $200^{circ}C;(5;min);{ ightarrow};5/min;{ ightarrow};280^{circ}C;(10;min)$ was developed. The analysis of fucosterol in P. siliquosa was successfully carried out within 30 min.