In　recent　years,　micro/nano-scaled　separation　technique　has　attracted　increasing　attention　due　to　its　inherent　advantages.　The　porous　layer　open　tubular　(PLOT)　capillary　column　is　an　important　micro-column　form.　Compared　to　wide-bore　PLOT　capillary　columns　(inner　diameter　＞　25　mu　m),　the　PLOT　capillary　columns　with　narrow　inner　diameters　yield　higher　separation　efficiencies　and　lower　reagent　consumption.　In　this　paper,　the　preparation　methods　for　porous　layer　open　tubular　capillary　columns　with　narrow　inner　diameters,　less　than　or　equal　to　25　mu　m,　are　reviewed.　Detection　techniques　combined　with　mass　spectrometry　and　their　applications　in　liquid　chromatography　are　also　discussed.