This paper investigates the preparation of the micro-nanoscale municipal solid waste incinerator (MSWI) ashes by using ball mills (PM 100). The physiochemical properties of MSWI ashes such as particle size, mineral compounds and metal content were further characterized by X-ray powder diffractometer (XRPD), X-ray energy dispersive spectrometer (EDS), field-emission scanning electron microscope (FE-SEM) and induced coupled plasma optical emission spectrometer (ICP-OES). In addition, titrations were carried out to obtain the potential metal release of MSWI ashes in MSW and distilled water at different pHs. Batch anaerobic digesters were also conducted to test the MSWI ash as catalyst in the co-digestion process of MSW and MSWI ashes. Results showed that micro-nanoscale size of MSWI ashes could be obtained by ball mill grinding and was verified by EDS analysis and laser particle size analyzer although some agglomeration phenomenon were found. Metals releases were found higher with pHs lower than 3. Gas accumulation in the batch anaerobic digesters also showed that suitable ratios of MSWI ash addition was found to show beneficial effects, however, higher than a critical amount of MSWI ash was found to exert a detrimental effects on anaerobic digestion.