In this study composition of organic matter and its variations in marine sediments of northwestern Arabian sea has been discussed. This paper presents the geochemical analysis of organic carbon content, C/N and d13 stable carbon isotope. The primary objective was to investigate the organic matter in sediments below an upwelling area. Undisturbed sediments (Piston core NIOP-486) of late Pleistocene time was collected during Netherlands Indian Ocean Program (NIOP-1992-93). The core NIOP486 was raised from a depth of 2077 meters near the Owen ridge. This core records deposition history of last 200,000 years and includes 4 warm and 3 cold periods. The distribution of organic carbon content in studied core shows cyclicity during glacial and interglacial stages. The source of organic matter and variations in glacial/interglacial stages are discussed. C/N ratio and d13 Corg isotope results are described to assess the relative proportions of terrestrial and marine organic matter.