Mutations of Cu-Zn superoxide dismutase (SOD1) have rarely been identified in Chinese patients with amyotrophic lateral sclerosis (ALS). We recently initiated a program to screen mutations of SOD1, TARDBP, and C9orf72 genes, the most commonly mutated genes in ALS patients in Western countries, in Chinese ALS patients. In this study, we report a novel missense SOD1 mutation with a substitution of tryptophan for cysteine at the seventh amino acid (p.C7W, traditionally named p.C6W) based on HUGO Gene Nomenclature in a familial ALS pedigree. We also found that the activities of SOD1 were significantly decreased in the C7W patient and the carriers of the family, compared with the SOD1 activities of normal family members. Compared with reported C7G and C7S patients, analysis of phenotype revealed relatively mild disease phenotypes in C7W patients, which is correlated with less deteriorated alteration in protein structure. Like those of many other familial ALS families, variable clinical phenotypes in the C7W intrafamily suggest that potential genetic modifiers may contribute to this disease.