Machado-Joseph disease (MJD) is relatively prevalent among the Yemenite Jewish subpopulation living in Israel. Currently, there is no treatment able to modify the disease progression. Trehalose is a disaccharide with protein-stabilizing and autophagy-enhancing properties. In animal models of MJD, trehalose showed reduction of cerebellar lesion size and improved motor function. This study was designed to be a proof-of-concept, phase 2 study lasting 6 to 12 months, to determine the safety, tolerability, and efficacy of weekly IV administration of 15 g or 30 g 10% trehalose solution in 14 MJD patients. Primary endpoints were safety and tolerability, which were assessed by various clinical and laboratory tests. Secondary endpoints were changes in the Scale for Assessment and Rating of Ataxia (SARA) score, Neurological Examination Score for Spinocerebellar Ataxia (NESSCA), time to do 9-hole peg test (9HPT), time to do 8-meter walk (8MW), and quality of life assessed by the World Health Organization Quality-of-Life Questionnaire-BREF (WHOQoL-BREF). Trehalose was well tolerated, and no serious drug-related adverse events were noted. The average SARA score, NESSCA, and time to do 9HPT and 8MW and the WHOQoL-BREF for all patients remained stable at 6 months. Six patients received treatment for as long as 12 months and continued to remain stable on all the above tests. IV trehalose seems to be safe in humans and probably effective to stabilize neurological impairment in MJD.