Abstract: The conventional methods for the determination of radioactivity of total α and total β in mineral water was improved by using only one portion of sample instead of taking two separate portions in the usual procedures,and by performing the determination of total α and total β simultaneously.The radio active isotopes in mineral water sample (1 to 5 L,acidified with a small amount of HCl previously) were pre-concentrated in the residue remained after evaporation with H2SO4 to dryness.The residue was ashed at 450 ℃ for 2 h,and its mass was taken accurately.Radio active source in the residue should conform to the rules of “thicker than the effective thickness” and “less than the maximum quantity of sample taken”.Time of measuring an influential factor to both the detection limit and the relative deviation of determination,was also discussed.