The present study aims to systematically describe mental practice (MP) in music memorization, with regard to individual differences in the use of different MP strategies and their performance outcomes. Sixteen pianists were studied while they memorized piano pieces. Each subject memorized two pieces, either via MP or physical practice (PP). In order to keep the setting as ecologically valid as possible within the experimental setup, we allowed subjects to freely apply their preferred MP strategies with the exception of physically playing a real piano. Practice and performances were video documented and expert rated; practice strategies were reported in researcher-developed questionnaires. The use of MP alone led to successful music learning. MP combined with PP produced results that were indistinguishable from those following PP alone. Pitch imagery and structural analysis were associated with better post-MP performance. Results are discussed in the frame of expert memory theory (Chase & Simon, 1973; Chaffin, Logan, & Begosh, 2009) and practical implications for musicians are provided.