Transient photoconductivity of the two polar surfaces of ZnO single crystal has been studied by using a fast-pulse technique. When ZnO crystal was irradiated by an ultraviolet (UV) light pulse, an obvious Dember effect was observed for both polar surfaces. The sign of the Dember effect indicated that the dominant photocarriers were electrons. Additionally, two distinct differences in UV photoconductivity were observed for the two polar surfaces. First, photocurrent Q was much larger for the O surface than for the Zn surface. The ratio of Q(O) to Q(Zn) was about 100 when the applied electric field E was perpendicular to the c-axis and about 30 when E was parallel to it. Second, the excitation light intensity I dependence was quite different. While the photocurrent of the O surface was proportional to I, the photocurrent of the Zn surface was proportional to I-1/2. These results indicated that the recombination processes of photocarriers were quite different between O and Zn surfaces; namely, the direct recombination process was dominant at the Zn surface, while the recombination centers were dominant at the O surface.