Contaminated soils are subject to diurnal and seasonal temperature variations during on-siteex-situbioremediation processes. We assessed how diurnal temperature variations similar to that in summer at the site from which petroleum hydrocarbon-contaminated soil was collected affect the soil microbial community and the extent of biodegradation of petroleum hydrocarbons compared with constant temperature regimes. Microbial community analyses for 16S rRNA andalkBgenes by pyrosequencing indicated that the microbial community for soils incubated under diurnal temperature variation from 5°C to 15°C (VART5-15) evolved similarly to that for soils incubated at constant temperature of 15°C (CST15). In contrast, under a constant temperature of 5°C (CST5), the community evolved significantly different. The extent of biodegradation of C10–C16 hydrocarbons in the VART5-15 systems was 48%, comparable with the 41% biodegradation in CST15 systems, but significantly higher than CST5 systems at 11%. The enrichment ofGammaproteobacteriawas observed in thealkBgene-harbouring communities in VART5-15 and CST15 but not in CST5 systems. However, theActinobacteriawas abundant at all temperature regimes. The results suggest that changes in microbial community composition as a result of diurnal temperature variations can significantly influence petroleum hydrocarbon bioremediation performance in cold regions.