A method of measuring quality of stem cells useful as therapeutic agents through real-time analysis, comprising: isolating desired cells in vitro; measuring a glutathione (GSH) level in the isolated cells; and determining cell quality according to the glutathione level, wherein determining cell quality according to the glutathione level is performed according to one or more selected from the group consisting of the following evaluation parameters: i) glutathione mean or median level (GM) of cells; ii) glutathione heterogeneity (GH) of cells; and iii) glutathione regeneration capacity (GRC) of cells, wherein the GM is calculated as the mean or median value of a cellular FreSH-tracer ratio (FR), the GH is calculated as the coefficient of variation or the robust coefficient of variation of cellular FR, and the GRC is a value obtained by real-time monitoring of FR or F510 after living cells are treated with an oxidizing agent, and is calculated by dividing a value obtained by subtracting a second area under the curve (AUC) of a group treated with a second oxidizing agent from a first AUC of a group treated with a first oxidizing agent by a value obtained by subtracting the second AUC of the group treated with the second oxidizing agent from a third AUC of a naive control and multiplying the resulting value by 100, wherein the F510 is a fluorescence emission spectrum of 510 nm, the F580 is a fluorescence emission spectrum of 580 nm, and the FreSH-tracer ratio (FR) is F510/F580, and wherein the measurement of a glutathione level is performed by adding Chemical B-4, B-5, B-6, B-7 or B-8 below: isolating desired cells in vitro; measuring a glutathione (GSH) level in the isolated cells; and determining cell quality according to the glutathione level, wherein determining cell quality according to the glutathione level is performed according to one or more selected from the group consisting of the following evaluation parameters: i) glutathione mean or median level (GM) of cells; ii) glutathione heterogeneity (GH) of cells; and iii) glutathione regeneration capacity (GRC) of cells, i) glutathione mean or median level (GM) of cells; ii) glutathione heterogeneity (GH) of cells; and iii) glutathione regeneration capacity (GRC) of cells, wherein the GM is calculated as the mean or median value of a cellular FreSH-tracer ratio (FR), the GH is calculated as the coefficient of variation or the robust coefficient of variation of cellular FR, and the GRC is a value obtained by real-time monitoring of FR or F510 after living cells are treated with an oxidizing agent, and is calculated by dividing a value obtained by subtracting a second area under the curve (AUC) of a group treated with a second oxidizing agent from a first AUC of a group treated with a first oxidizing agent by a value obtained by subtracting the second AUC of the group treated with the second oxidizing agent from a third AUC of a naive control and multiplying the resulting value by 100, wherein the F510 is a fluorescence emission spectrum of 510 nm, the F580 is a fluorescence emission spectrum of 580 nm, and the FreSH-tracer ratio (FR) is F510/F580, and wherein the measurement of a glutathione level is performed by adding Chemical B-4, B-5, B-6, B-7 or B-8 below: <EOS>