Landfill sites are hard to obtain in Taiwan. Municipal solid waste (MSW) in the closed landfill sites has high combustible content and calorific value (CV). Therefore, activating the closed landfill sites as municipal mine sites to prolong their service life will promote a sustainable environment. This study transforms combustibles from the closed municipal landfill sites of different landfill ages (LAs) into refuse-derived fuel (RDF) through pretreatment and squeeze forming equipment, so to investigate the characteristics of the MSW of different LAs, and the manufacturing conditions and firing behaviour of RDF. The results indicate that the proportion of the combustibles in MSW declines as the LA grows, and therefore the proportions of both incombustible materials and soil and debris correspondingly increased. The LA of the MSW is thus negatively correlated with the CV. The MSW at the LA of 10 years still has high potential as fuel material. The fixed carbon initiation temperatures (i.e. ignition temperatures) of combustibles of the MSW at the LAs of 1 year, 5 years and 10 years are 259°C, 256°C and 245°C, respectively. The CV and flame temperature of the RDF increase slightly with the increasing squeeze temperature (ST) at 100–120°C, but it will decrease when the ST reaches 130°C. Therefore, this study recommends the squeeze pressure of the RDF as 41.65 ± 8.24 kg cm⁻², ST 110°C and combustible size 10–20 mm.