Amyotrophic Lateral Sclerosis (ALS) is a fatal adult onset neurodegenerative disease, causing the progressive degeneration of motor neurons. Mutations in the gene encoding fused in sarcoma (FUS) are responsible for causing a subset of ALS cases. In neurons, FUS expression is predominantly nuclear however, mutations lead to its cytoplasmic translocation followed by inclusion formation. Both oxidative and ER stress are implicated early in ALS pathology and the interplay between them is poorly understood. However both processes cause mutant FUS to co-localise within stress granules, which are thought to be early precursors to inclusions. In response to ER stress protein disulphide isomerase is upregulated, and shown to be protective against FUS ALS pathology. However it is unknown whether this protective effect is a result of the chaperone or disulphide interchange activity of PDI. This study investigated the cellular pathogenic mechanisms induced by FUS and examined whether the chaperone or disulphide interchange activity was responsible for the protective effect of PDI. This study shows that induction of either oxidative or ER stress causes mutant FUS to recruit to stress granules and translocate to the cytoplasm. Also, induction of oxidative stress was found to induce ER stress. Both the chaperone and disulphide interchange activity of PDI decreased mutant FUS cytoplasmic translocation and reduced in ER stress, demonstrating that both activities of PDI were protective against ALS FUS pathology. These findings further support the notion that interplay between oxidative and ER stress exists in ALS and raises the question of whether abnormal disulphide bonding occurs in FUS.