The photodegradation of a stearic acid (SA) microcrystal on an amorphous titania film surface scattered with submicrometric anatase domains is observed using a Reflected Light – Differential Interference Contrast (RL-DIC) microscopy. The SA microcrystal, grown from a saturated solution, is flat and rhombus-shaped with acute angle of 55° in agreement with the C-polymorph of SA crystal. We observe that the photodegradation initiates at the anatase microdomains under the microcrystal and creates SA holes in the shape of truncated-rhombus or elongated-hexagons having the same orientation and symmetry as the SA microcrystal. The expansion of the SA holes is ascribed to a photodegradation mechanism mediated by the photogeneration and surface diffusion of radical species across the gap between the anatase microdomain and the edges of the SA holes. A detail kinetic study of the SA holes expansion shows that the surface area of the SA holes scales almost linearly with UV exposure time in good agreement with an apparent zero-order kinetics. The morphology and the expansion kinetics of these holes are rationalized through the orientation dependence of the reactivity of the molecules with the radical species.