Asphaltenic and other polar organic compounds in crude oil form aggregates, precipitate, adhere to surfaces, block rock pores, and severely alter the wetting characteristics of mineral surfaces within the reservoir, hindering oil recovery efficiency. Tremendous experimental efforts have been done to investigate asphaltene aggregation and precipitation from crude oil. Most of these works were carried out on planar mineral substrates or in bulk solution. However, not many direct measurements have been done in a small confined microsized pore. Examining asphaltene aggregation in a microcapillary might represent asphaltene deposition in reservoir pores better than the investigations on flat surfaces. Therefore, in this study we employ new methods to directly visualize the asphaltene aggregation process and investigate the kinetics of asphaltene aggregation in a microcapillary. The asphaltene aggregation behavior can be described by diffusion-limited-aggregation (DLA) and reaction-limited-aggregation (RLA) models. Effects of concentration of asphaltene precipitant and temperature were investigated. The results indicate that the concentration of precipitant has a significant effect on the aggregation rate and aggregation mechanism. The asphaltene aggregation is faster at higher concentrations of precipitant. The kinetics of asphaltene aggregation at higher precipitant concentrations is predominantly controlled by the DLA mechanism. The slow RLA mechanism mainly dominates the aggregation process at lower concentrations of precipitant. The results were also compared with those measured on a flat surface in bulk solution in this study. At higher concentration of precipitant, the effect of confinement from the microsized capillary might lead to different asphaltene aggregation behaviors in a microcapillary from those in bulk solution.