A new HPLC method has been developed for measuring clonazepam (CZP) in plasma, using a reversed-phase non-porous silica column packed with 2 μm particles. CZP in plasma was first purified with a column extraction technique and injected onto a non-porous silica column. The calibration curve was linear from 5—200 ng/ml. The recoveries of CZP added to plasma were more than 94.0%, with a coefficient of variation in the range of 5.1—13.8%. We developed a rapid routine method using a non-porous silica column that was accurate and improved solvent consumption in the measurement of CZP.