Objective: Flame at. spectrophotometry was established for the determination of magnesium in calcium supplements,and the content of magnesium in several calcium supplements was determinedOtherwise,the results were compared with the content demonstrated by magnesium and alkali metal salts.Methods: With the condition which magnesium lamp was used with the wavelength at 285. 2 nm,the slim width was set at 0. 2 nm,and the lamp current at 0. 3 m A,the calibration curve method and the standard additive method was used for the determination of magnesium in calcium supplements by flame at. absorption spectrometry.Ignition residue was used for determination of limit of magnesium and alkali salts.Results: There are some differences in the results obtained by different determination methods,but these results show the same trend between different samples.Conclusion:Compared with the method for determination of magnesium and alkali metal salts,both standard curve method and standard additive method can accurately determine the content of magnesium in calcium supplements.As samples with higher content of magnesium,the calibration curve method is better than the standard additive method in the case of eliminating interference by using anti-interference agents.