Although the effects of habitat size and shape on ecological processes have been well studied, the importance of habitat orientation (i.e., the geometrical feature of habitat placement that describes how a habitat is placed in space) has been largely overlooked for decades. Here, we varied the orientation of cuboid chambers (with correspondingly small, medium and large sides as the chamber base) in a microcosm experiment involving a phytoplankton-zooplankton (Chlorella pyrenoidosa-Ceriodaphnia quadrangula) system at two volume scales (64 mL and 512 mL) to determine the effect of habitat orientation on the swimming activity and grazing rate of C. quadrangula. At a given chamber volume, the grazers spent more time in swimming vertically and swam slower (particularly in the horizontal direction) in the tall (small-based) chamber compared with the short (large-based) ones. Moreover, grazing rates of C. quadrangula were significantly lower in the tall chambers than short ones regardless of experimental time, consistent with the positive relationship between average swimming velocity and grazing rate. Our data indicate that habitat orientation may affect animal activity and foraging success, and we therefore suggest that habitat orientation deserves much more attention in future studies.