When fine particles suspended in the gas oil feed come in contact with the hydrotreating catalyst at the reaction conditions, there is a change in the surface chemistry of the particles and they settle on the catalyst bed. The increase of the particle concentration in the catalyst bed leads to pressure drop in the reactor and eventually to catalyst deactivation. In this study, the impacts of process parameters such as temperature and pressure on particle deposition were studied. Also, the impact of particle size, reaction time and catalyst regeneration studies were conducted. For rationalization of the batch reactor set-up, used for hydrotreating, the catalyst was packed in a catalyst basket with a forced longitudinal feed flow through the packed catalyst bed in the basket. The spent catalyst was examined using various characterization techniques to understand the physical and chemical impacts of particle deposition on the hydrotreating catalyst. It was found that temperature significantly impacts particle deposition. Asphaltene coated kaolin has a preferential deposition on the reactor assembly and thus the overall bed deposition this case was less as compared to uncoated kaolin. When there was no catalyst packed in the basket, there was negligible bed deposition. Thus, it could be inferred that catalyst-fines interaction is chemical in nature.