This thesis study investigates the effects of differently prepared oxide substrates on gas sensing behaviors of graphene gas sensor. Explanations for why such effects happen are also revealed through experimental works. The thesis consists of a detailed study of gas sensing behaviors from graphene gas sensors using different oxide substrates. Subsequent material study of these oxide substrates is conducted. Moreover, a metal-graphene contact resistance study is included in the thesis as well, presenting the effort to make a better graphene gas sensor system.