Objective: Amyotrophic lateral sclerosis is an incurable disorder mainly characterized by motoneuron degeneration. Mutations in the superoxide dismutase 1 (SOD1) gene account for 20% of familial forms of the disease. Mutant SOD1 exerts multiple pathogenic effects through the gain of toxic properties in both neurons and glial cells. Here, we compare AAV-based gene therapy suppressing expression of mutant SOD1 in either motoneurons or astrocytes. Methods: AAV vectors encoding microRNA against human SOD1 were administered to (G93A)SOD1 mice either by intracerebroventricular injections in pups or by lumbar intrathecal injections in adults. Vector systems were designed to suppress SOD1 expression predominantly in either spinal motoneurons or astrocytes. Electrophysiological and behavioral tests were performed on treated animals to evaluate disease progression. Results: Following vector injection in (G93A)SOD1 pups, efficient silencing of SOD1 expression was achieved in motoneurons and/or astrocytes. Most complete protection of motor units was obtained when targeting human SOD1 predominantly in motoneurons. Suppressing SOD1 mainly in astrocytes led to preserved muscle innervation despite only partial protection of spinal motoneurons. In both cases, injection in pups led to full recovery of neuromuscular function and significantly prolonged survival. Vector injections in adult mice also achieved significant protection of neuromuscular function, which was highest when motoneurons were targeted. Interpretation: These results suggest that AAV-mediated SOD1 silencing is an effective approach to prevent motoneuron degeneration caused by SOD1 mutation. AAV vectors suppressing SOD1 in motoneurons delay disease onset and show effective neuroprotection. On the other hand, AAV-based SOD1 silencing in astrocytes rescues neuromuscular function following initial denervation.