The use of disposable diapers is increasing every year, increasing generated diaper wastes every year. In Surabaya, diaper wastes have become an important issue when they are not treated properly. These diaper wastes will end up in water bodies and cause pollution. One of the technologies that can be used to treat diaper wastes is composting. Disposable diaper wastes consist of high lignocellulose and C content. It is necessary to mix diaper wastes and other wastes with high N content as a co-substrate, so that the optimum C/N ratio of composting can be achieved. In this research, vegetables wastes were used. The Objective of the research was to determine the effect of vegetable wastes adding as a co-substrate in composting of disposable diapers and volatile solid (VS), C-organic, and Total Nitrogen (TN) content changed during the composting process. The research was carried out with three variables mixtures of diaper wastes and vegetable wastes. Two control consist of 100% diaper wastes and 100% vegetables wastes. The Total weight of raw materials was 10 kg for each reactor. The composting process is carried out aerobically with a composting time of 60 days. The results showed that vegetable wastes have the potential to be used as a co-substrate for diaper wastes. The content of C-organic, VS and total nitrogen decreased. All of the parameters include C/N ratio meet the Indonesian Standard of compost.