Alkylated polycyclic aromatic compounds (PACs), which are rich in dibenzothiophenes, are present in natural and reclaimed aquatic environments in the oil sands region of northern Alberta (Canada). An oil sands-derived PAC extract has been shown to induce signs of blue sac disease in Japanese medaka (Oryzias latipes) embryos. Information regarding exposure to and effects of oil sands PACs is available, but little of this information concerns the impact of modifying factors. The present study focuses on the effect of simulated solar radiation on oil sands-derived PAC toxicity to Japanese medaka embryos. Photomodification of the oil sands PAC extract caused reduced toxicity with an increase in the duration of ultraviolet (UV) exposure. Generally, mortality and developmental endpoints and, to a lesser extent, growth were affected by photomodification. Coexposures of the PAC mixture and UV caused slight increases in toxicity for mortality and embryonic developmental endpoints at the longest duration of UV exposure tested (16 h). Based on the modest phototoxicity of the oil sands PAC extract to Japanese medaka embryos, enhanced toxicity associated with UV irradiation may not be a concern for embryos of fish species that are common to the oil sands region. However, testing the effects of differing levels of UV irradiation on larval fish and invertebrates that may differ in their PAC bioaccumulation would improve our understanding concerning the importance of UV irradiation as a modifying factor in oil sands environmental risk assessment.