The purpose of this study was to examine the effects of mental practice, physical practice, and mental and physical practice combined on the ability to create melodic jazz solos within chord progressions, possessing relatively simple or complex harmonic characteristics. We also explored whether improvisation achievement varied as a function of general mental imagery ability. Fifty-six jazz studies majors from two large North American universities were randomly assigned to one of three experimental conditions (physical practice, mental practice, or physical and mental practice combined) and tasked with preparing melodic improvised solos over two sets of chord changes that varied in complexity (i.e., simple vs. complex). The participants’ solos were rated for melodic jazz improvisation achievement by two expert-level professional jazz artists. Participants also completed a self-report questionnaire that captured the degree of the vividness of their visual, aural, cutaneous, kinesthetic, and organic mental imagery. We did not find significant differences in melodic improvisation achievement as a function of practice condition nor did we find that chord progression complexity moderated the effect of practice condition. However, significant differences were detected as a function of chord progression complexity. Theoretical avenues for designing future experiments are discussed in-depth with respect to the typical practice approaches jazz musicians use when developing improvised solos, issues of closed- versus open-class motor skills, cognitive load, and expert memory storage and retrieval.