Management of rice straw is of environmental concern because it significantly affects methane (CH₄) emissions from rice paddies. To evaluate straw-application effects on paddies those have different cultivation histories, we measured CH₄ emissions in continuously cultivated rice paddy (CP) and recently converted paddy (RP) (from soybean cultivation) with rice straw treatments (+S). Further, we hypothesized that changes in i) soil Fe (III) reduction and ii) population dynamics of methanogens were responsible for the different responses of CH₄ emissions due to straw application between CP and RP. Methane (CH₄) emission from CP+S was 2-fold larger than that from RP+S, although relative enhancement was higher in later (492%) than the former (289%) compared with no straw application. Stoichiometric evaluation revealed that applied rice straw acted as an exogenous source of electron donor for CH₄ production, especially in CP. Our results showed that the increase in CH₄ emissions by straw application was much greater in continuous than short term paddy.