Nonthermal plasma chemical decomposition of bromomethane (CH3Br) was investigated with a coaxial type packed-bed plasma reactor. It has been demonstrated that plasma chemical processing is an effective approach to decompose CH3Br in a wide concentration range. It has been shown that CH3Br decomposition reactivity depends on reactor operating factors such as background gas, O2 concentration, and humidification. Higher decomposition efficiencies can be obtained in dry N2. However, organic byproducts such as BrCN are concurrently produced under deaerated conditions. Water suppresses CH3Br decomposition and also affects the yields of COx (CO and CO2) and organic byproducts due to the involvement of some active species generated from water. The presence of O2 retards CH3Br decomposition by quenching high-energy electrons, while it suppresses organic byproducts and improves COx yield. The reacted carbons in CH3Br are recovered as COx almost quantitatively in air. Higher CO2 selectivities cannot be achieved by increasing O2 concentration. NOx formation, which is accompanied by CH3Br decomposition, can be effectively suppressed by decreasing O2 concentration down to 2%. Furthermore, reaction mechanisms are discussed by comparing the reactivities of CH3Br and its congeners.