Gel chromatography with Sephadex LH-60 has been combined with inductively coupled plasma emission spectrometry (ICP) for selective detection and determination of molecular weight of organosilicon compounds. Application of this method to the field samples and organosilicon containing products were described ; field samples were sludge from night soil treatment plant, river sediment and ash from municipal incinerator, and organosilicon containing products were anti-foaming agent, car polish and cosmetic (cologne). The organosilicon concentration ranged from 0.19 ppm to 89 ppm in field samples, and from 1300 ppm to 47000 ppm in the products. The average molecular weight of organosilicon compounds extracted from the field samples were >6000. The organosilicon compounds in incineration ash were made up of a broad molecular weight distribution, although they consisted mostly of high molecular weight compounds. The organosilicon compounds were ascertained to be polydimethylsiloxane by infrared spectroscopy. The organosilicon compounds in cosmetic (cologne) were extremely low molecular-weight compounds, and identified to be octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane.