The wine industry generates a large amount of wastes, including grape marc and vinification lees. These substances can be used to produce enzymes or other food additives. Composting could be a successful strategy for the sustainable and complete recycling of grape marc. In this work, the mesophilic biodegradation of grape marc during 60 d under microaerobic conditions using several ratios of seeds, skin, and stem were studied. The presence of Penicillium spp. was detected at the beginning of the composting. Changes in chemical and biological parameters were evaluated. Biodegraded grape marc with stem showed the best organic matter properties (C/N ratio of 14 and N content of 37 g/kg) and a germination index of 155% for the growth of ray grass seeds. The results suggest that the biodegraded of grape marc could be used as fertilizer, especially for ray grass crops.