Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by the selective death of motor neurons. Mutations in the SOD1 gene are responsible for a familial form of ALS (FALS). Although many studies suggest that mutant SOD1 proteins are cytotoxic, the mechanism is not fully understood. To investigate the role of mutant SOD1 in FALS, human SOD1 genes were fused with a PEP-1 peptide in a bacterial expression vector to produce in-frame PEP-1-SOD fusion proteins (wild type and mutants). The expressed and purified PEP-1-SOD fusion proteins were efficiently transduced into neuronal cells. Neurones harboring the A4V, G93A, G85R, and D90A mutants of PEP-1-SOD were more vulnerable to oxidative stress induced by paraquat than those harboring wild-type proteins. Moreover, neurones harboring the mutant SOD proteins had lower heat shock protein (Hsp) expression levels than those harboring wild-type SOD. The effects of the transduced SOD1 fusion proteins may provide an explanation for the association of SOD1 with FALS, and Hsps could be candidate agents for the treatment of ALS.