Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disorder, characterised by progressive motor neuron degeneration and muscle paralysis. Heat shock proteins (HSPs) have significant cytoprotective properties in several models of neurodegeneration. To investigate the therapeutic potential of heat shock protein 27 (HSP27) in a mouse model of ALS, we conducted an extensive characterisation of transgenic mice generated from a cross between HSP27 overexpressing mice and mice expressing mutant superoxide dismutase (SOD1(G93A)). We report that SOD1(G93A)/HSP27 double transgenic mice showed delayed decline in motor strength, a significant improvement in the number of functional motor units and increased survival of spinal motor neurons compared to SOD1(G93A) single transgenics during the early phase of disease. However, there was no evidence of sustained neuroprotection affecting long-term survival. Marked down-regulation of HSP27 protein occurred during disease progression that was not associated with a reduction in HSP27 mRNA, indicating a translational dysfunction due to the presence of mutant SOD1 protein. This study provides further support for the therapeutic potential of HSPs in ALS and other motor neuron disorders.