In this study, artificial rainfall was applied to a partially frozen Andisol soil, and the effects of the subsoil's physical conditions, prefreeze moisture condition, and soil compaction on surface runoff and soil loss were studied. The soil, an Andisol from a mountainous region of Japan, was packed into a plastic box to a thickness of 0.08 m to attain a predetermined moisture condition and dry bulk density, then stored in a freezer at −30°C overnight to create a sample representative of frozen subsoil. Twenty millimeters of unfrozen soil were added on top of the frozen subsoil to simulate a thawing surface layer. During the simulated rainfall (42 mm h−1) experiment, surface runoff, soil loss, and seepage from outlets at the front wall of the downslope end of the box were sampled periodically. In the early stage of rainfall, the impermeable frozen subsoil increased surface runoff and soil loss, and seepage occurred at the downslope end of the box, indicating saturation of the near‐surface, unfrozen soil. During the early stage of the rainfall, soil loss was particularly greater than during the latter half of the rainfall experiment although both showed a similar surface runoff rate. Saturation of the near‐surface soil was the reason for the greater soil loss rate, while a surface seal restricted soil loss by surface runoff during the latter half of the rainfall experiment.