Gastrointestinal stromal tumors (GISTs) comprise about 80% of mesenchymal neoplasms in the gastrointestinal tract. Although imatinib mesylate is the preferred treatment, the development of drug resistance highlights the need for novel therapeutic strategies. Recently, we have identified the microphthalmia-associated transcription factor (MITF) as a critical player in pro-survival signaling and tumor growth. This study investigates the effects of MITF inhibition using ML329, an MITF pathway inhibitor, on GIST cell viability and in NMRI-nu/nu mouse xenograft models. ML329 suppresses growth in imatinib-sensitive (GIST-T1) and -resistant (GIST 430/654) cell lines, impairs MITF targets such as BCL2 and CDK2, and induces S-G2/M cell-cycle arrest. , ML329 is well tolerated and significantly reduces tumor growth in established imatinib-sensitive and -resistant GIST models. These findings underscore the importance of MITF in GIST growth and support its inhibition as a promising therapeutic approach.