Heptane-induced asphaltene precipitation from crude oil and its deposition in a vertical transparent microchannel is investigated. The amount of asphaltene deposited on a transparent channel wall is quantified using a non-intrusive flow visualization technique based on reflected light intensity and image analysis. Asphaltene deposits strongly affect the reflected light intensity through the change of mixture color in the recorded images. An empirical equation is developed to correlate the intensity of the light absorption to the thickness of the deposited asphaltene in a transparent microchannel. Non-uniform deposition along the longitudinal direction of the microchannel is also characterized.