An experimental study by Hyun and Luck suggests that object working memory, but not spatial working memory, is employed during mental rotation. In contrast, correlational research points to the relevance of spatial working memory in mental rotation. Considering these somewhat conflicting results and the fact that a small sample was acquired in the study of Hyun and Luck, a replication of their study was conducted. Additionally, potential sex effects were explored. We collected (usable) data from 213 individuals across two experiments. All participants performed a mental-rotation task alone, a working-memory task alone, and both tasks concurrently. We expected greater rotation-dependent interference between tasks when the working memory task concerned object features (Experiment 1) than when it concerned spatial locations (Experiment 2). In Experiment 1, dual-task interference was observed in working-memory accuracy. In Experiment 2, there were interference effects in both mental rotation accuracy and working-memory accuracy. However, interference did not differ between experiments. Moreover, interference was not rotation dependent in either of the experiments. Thus, we could not replicate the findings of Hyun and Luck. No sex differences were found in exploratory analyses. The general interference effects found in this study may reflect the involvement of visual working memory in the processing and decision-making stages of the mental rotation of letters. This study underscores the need for further research to fully understand the role of visual working memory in mental rotation, especially with more complex stimuli.