The effects of different music experiences have been presented in several systematic reviews. On the other hand, musical improvisation, one of the major musical experiences in music therapy has not yet been addressed in systematic reviews. The aim of this article is to conduct a systematic review to evaluate the effectiveness of musical improvisation in music therapy randomized controlled trials (RCTs). Altogether, it was found 10 studies, 85 outcomes and 50 of these (58.82 %) were statistically significant (P<0.05) The studies reviewed presented a good (not perfect) standard of excellence in terms of methodological quality (average of 3.9 on a scale of 1 to 5) evaluated by Jadad Scale (instrument of methodological quality). Owing to the absence of similar research questions, it was not possible to calculate the meta-analysis estimative. Therefore, further studies with higher methodological quality, greater quality of data and similar research questions are needed to define the role of musical improvisation in music therapy according to RCTs.