Abstract: The on-line internal standard with direct introduction of organic solvent method was established for the determination of silicon in coker distillates by inductively coupled plasma optical emission spectrometry (ICP-OES). The effect of twelve different silicon organic compounds on the response sensibility was tested. Among of them, the trimethylsilanol, triethylsilane, dimethoxydimethylsilane and hexamethyldisiloxane show higher sensibility than other eight compounds, and the ratios of measured and theoretical value (about 2 ?g/g) are 5.0, 3.4, 4.2 and 4.1, respectively. However, these four compounds have little effect on the determination of silicon in real coker distillates due to very low concentrations. The ring siloxanes are the main organic silicons in real coker distillates, the response sensitivity of these compounds are close to each other. The adding standard recoveries of Si in coker gasoline and coker diesel are 101% and 98.4%, respectively. The limit of detection of the method is 0.03 ?g/g. and therefore, the ICP-OES can be used for quantitative analysis of silicon content in the coker distillates.