Abstract: Objective To establish an analytical method for simultaneous determination of 24 metals in indoor air particulate matter <2.5 μm in aerodynamic diameter (PM_2.5).Methods Indoor air PM_2.5 samples were collected with polytetrafluoroethylene (PTEF)filter at 6 sampling points set in ordinary residential rooms during January and February (the months with frequent haze weather and Spring Festival period when fireworks and firecracker show being not prohibited)in Beijing city.The 24 metals (berylliumBe,vanadiumV,aluminiumAl,chromiumCr,manganeseMn,cobaltCo,nickelNi,copperCu,zincZn,arsenicAs,seleniumSe,molybdenumMo,silverAg,cadmiumCd,antimonySb,bariumBa,thalliumTl,plumbumPb,uraniumU,sodiumNa,magnesiumMg,potassiumK,calciumCa,and ferrumFe)in the PM_2.5 samples were digested with microwave oven and then detected with inductively coupled plasma-mass spectrometry (ICP-MS).Results The medians of the concentrations of the 24 metal elements ranged from 0.01 ng/m³ (Be) to 281.40 ng/m³ (K) for the indoor air PM_2.5 samples collected in clear days,0.01 ng/m³ (U) to 2 472.00 ng/m³ (K) in haze days,and 0.01 ng/m³ (U) to 6 327.00 ng/m³ (K) in the days with fireworks and firecracker shows,respectively.The values of relative standard deviation for the determination were between 3.4% and 8.6% for the 24 metal elements,except for Al (17.1%),Na (20.4%),and Mg (12.8%).Conclusion A method with PTEF filter sampling,nitric-hydrofluoric-boracic acid-microwave digestion and ICP-MS was successfully established for simultaneous determination of 24 metal elements in indoor air PM_2.5 samples.