1. Global rising of average temperatures and increase in extreme climatic events may largely impact animal survival and reproduction. Yet, how variation in temperature may affect male fertility, in particular ejaculate traits, and whether this can in turn affect offspring fitness, is seldom addressed. Paternal effects may be of key importance as they could impact the rate and direction of evolutionary change in response to climate change. 2. We tested the effects of temperature experienced by males on sperm traits, and asked whether the paternal environmental temperature affected offspring phenotype. We further explored the potential for paternal effects to be adaptive, which would occur when offspring fitness increased under the same environmental conditions experienced by the fathers. We exposed male field crickets to high or low temperatures at two life stages, either throughout development or as adults, and tested sperm traits (number and quality) and offspring fitness (hatching success and survival). We further assessed sperm traits in offspring, after they had also been exposed to the same or different temperature experienced by their father. 3. We found that temperature affected sperm traits depending on the life-stage of individuals. When the exposure was given during adulthood, males exposed to high temperature produced less sperm and of lower quality compared to males exposed to the lower temperature, while if exposure was given during development males exposed to high temperature produced more sperm and of better quality compared to males exposed to low temperatures. Offspring fitness was significantly affected by paternal temperature, evidence for anticipatory paternal effects on sperm traits was not found. 4. Our study indicates that temperature can mediate cross-generational effects, and that paternal effects may be mediated by changes in temperature and therefore much more widespread in nature than previously assumed.