The increasing incidence of oil pollution together with thermal changes resulting from global warming has led to numerous impacts on marine organisms; therefore, understanding the effects of these factors on key organisms in the marine food chain is of great importance. Accordingly, the present study investigated the combined effects of temperature (as a climatic stressor) and pollution caused by Iranian crude oil on the copepod Harpacticoida sp. isolated from the Persian Gulf. In this context, survival, reproduction (the proportion of ovigerous adults and the proportion of produced nauplii), fecal pellet production, and body size of copepods exposed to different treatments—crude oil, dispersant, and oil–dispersant—were measured under simulated conditions across a range of temperatures (25, 28, and 31 °C). The results of this study showed that exposure of harpacticoid copepods to crude oil and dispersant, particularly in the combined treatment, had a significant negative effect on reproduction and female survival. At 26 °C, the control treatment showed a significant difference in the proportion of ovigerous copepods compared with the combined oil–dispersant treatment (p < 0.05), while the oil or dispersant treatments alone did not show a significant difference. At 28 °C, the greatest negative effect was observed in the combined treatment, and during days five to seven, only the control treatment showed a significant difference compared with the other treatments. At 31 °C, a significant difference was observed only on day six between the control and the other treatments.These findings indicate that the effects of oil compounds and dispersants intensify with increasing temperature and exposure duration; therefore, this study emphasizes that oil pollution and its associated chemical compounds can reduce copepod survival and reproduction and potentially exert negative effects on marine populations and ecosystems. The results of this research demonstrate that the simulta