Twenty-three mesozooplankton samples were taken by oblique tows through the ~160 m with a bongo net during September 2007 in the Colombian Pacific Ocean (OPC).The spatio-temporal variation and oceanographic conditions effects on the abundance and volumetric biomass variation of 5 size classes of copepods were evaluated.Temperature, salinity, dissolved oxygen and chlorophyll-a, per station, and their possible relation to the biomass and abundance of those organisms were analyzed.The water column was characterized by a mixed layer of ca., 30 m, a thermocline around 80 m and a bottom layer of cold water (17.4 ± 0.5 o C) and low oxygen concentration (1.36 ± 0.2 mg L -1 ).This stratification may have favored the retention of small-size copepods in the mixed layer.Furthermore, the presence of large size copepods in surface waters could be due to migratory behavior in the water column.The abundance reached 14,933 ind. 100 m -3 (1,641 mm 3 100 m -3 ), where 79% was composed of copepods with cephalothorax length < 1 mm.Their homogeneous distribution could be linked to the physico-chemical conditions of the surface layer in all the study areas.There was a strong correlation among the higher abundances and biomasses with waters with higher density and low concentration of chlorophyll-a. Key words: