Asphaltenes are the most polar molecules in crude oil and are responsible for a large number of deposition and fouling problems in the oil industry. The mechanisms by which asphaltenes deposit have not been fully elucidated, and the goal of this investigation is to reveal the underlying physics of the asphaltene deposition process. A new deposition apparatus was designed and constructed to investigate asphaltene deposition. The apparatus consists of a packed bed of stainless steel beads over which a mixture of oil and heptane is passed at a specified flow rate and run-time. The asphaltene deposition rate and the mass of deposit can be obtained along the packed bed. The dependency of the asphaltene deposition rate on concentration of unstable asphaltenes and on fluid flow velocity was studied. Experimental results show that a mass-transfer limited deposition model can explain the asphaltene deposition of nanometer-sized unstable asphaltenes in the viscous flow regime. This investigation sheds light on the asphaltene deposition process and provides a new tool that can be used to study asphaltene deposition.