Technical Abstract: Cholecystokinin (CCK) and the different molecular forms of CCK are well established as biomarkers for satiety. CCK hormone and the different biologically active and inactive molecular forms have been shown to influence food intake associated with satiety and are predominately secreted from the gut. Despite the importance of CCK in satiety, endogenous CCK-8 has not been well characterized in Syrian Golden hamsters. In this study, we have cloned and sequenced hamster CCK and identified and characterized endogenous CCK-8 from hamster plasma. Hamster CCK-8 is comprised of 8 amino acid residues which are highly conserved amongst other species. Following accurate identification and characterization of hamster CCK-8, we have developed a highly specific and sensitive immunoprecipitation based LC-MS/MS assay for its quantification. The present assay enables quantification of active CCK-8 over a concentration range from 0.1 to 2.5 ng/mL in hamster plasma samples. This range covers both the basal and postprandial levels of CCK-8. Assay accuracy (% RE) and precision (% CV) were measured at three concentrations on each of four days and did not exceed x.x and xx.x%, respectively. Additionally, the method was shown to be applicable for determining the increased concentration of endogenous CCK-8 in hamster plasma following being gavaged high fat diet compared to a low fat diet.