Most studies on the effects of climate change have been conducted on grain yield and composition; few have focused on seed germination and storage ability, especially in temperate crops. However, projected higher temperatures at the end of crop cycle are expected to affect not only seed nutritional quality but also seed germination and storage ability. In this study, experiments were conducted on wheat (Triticum aestivum L.) and pea (Pisum sativum L.) in controlled conditions to assess the effects of high maximum daytime temperatures, between 25°C and 35°C, on mother plants during grain filling or only during grain desiccation. Grain composition and seed characteristics related to germination and seed storage were investigated. When the stress occurred during grain filling, seed dry weight decreased, and protein and total fatty acid concentrations increased. Higher contents of vicilins in pea and polyunsaturated fatty acids in both crops were observed. Total starch content decreased in wheat. Sucrose : oligosaccharides ratio decreased, seed conductivity increased and germination was altered in both crops whenever the stress occurred. All of these modifications were mainly detrimental to the seed nutritional and end-use values. Further investigations should be carried out to assess genetic diversity, to characterise other species, and to introduce the impact of high temperatures on these seed characteristics into crop models.