For the determination of the low concentration of ²²²Rn in sea water, an improved ²²²Rn extraction and counting system was developed. The ²²²Rn in a 20 l sample bottle was extracted from sea water with helium and collected in a charcoal trap cooled with dry ice and alcohol. The ²²²Rn extraction is accomplished by two circulation loops in a closed system : one is the rapid extraction loop of ²²²Rn from sample water by violent gas bubbling and strong agitation, and the other is the adsorption loop of ²²²Rn with a cooled charcoal trap. Successively, the ²²²Rn was desorbed from the trap by heating and transferred to a scintilla-tion cell coated with ZnS(Ag). Following these procedures one can process a sample in 100 min with an overall efficiency (extraction-transfer-counting) of 57%. Some results of ²²²Rn and ²²⁶Ra concentrations in coastal sea water are reported.