The paper aims to analyse the results of long-term studies of dissolved and suspended organic matter content in the waters of the Northern Caspian and Middle Caspian in the Russian sector of the Caspian Sea. The paper analyses the main sources of input of organic matter, its seasonal and inter-annual variability, features of its spatial distribution and causes (allochthonous organic matter flow, production and destruction, water temperature, sea level changes, etc.) determining the spatial and temporal dynamics of organic matter content. The paper is written on the results of production environmental monitoring conducted at the licensed areas of LLC LUKOIL-Nizhnevolzhskneft in 2017-2021. The organic matter amount was estimated by organic carbon. The dissolved organic carbon concentration was found to vary from 0.10 to 9.30 mg/dm³ in the surface water layer and from 0.10 to 9.60 mg/dm³ in the bottom layer. The maximum enrichment of waters with dissolved organic matter was noted in the northern part of the water area. The concentration of suspended organic carbon in the surface water layer varied within 0.10-23.40 mg/dm³, whereas in the bottom water layer it ranged within 0.05-19.40 mg/dm³. The spatial distribution of suspended organic matter was characterized by seasonal shifts of the area with maximum concentrations northwards. The main factors affecting the organic matter content in water were water temperature, suspended matter concentration in water and hydrogen ion concentration. The level of dissolved and suspended organic matter has not changed in the last 20 years of studies. The dependence of dissolved and suspended organic matter concentrations on environment pH indicates the natural origin of the organic matter in the waters of the monitored sea area.