Extraction of oligonucleotides by, a cationic surfactant as investigated in a liquid-liquid extraction system. A cationic surfactant having two long alkyl chains proved to be effective for the extraction of oligonucleotides from an aqueous to an organic phase. Important parameters affecting the efficiency, of the extraction were the kind of surfactants, alcohol content, salt concentration, pH of the feed solution and the operational temperature. The sequence of oligonucleotides also affected the extraction behavior. Back extraction was successfully performed by adding proper alcohol and salt in the recovery phase.