Abstract: The foam separation of saponin from Sapindus mukorossi crude solution was studied. The foam which overflowed from the separation column was collected. The total saponin contents of crude solution and foam were determined by UV spectrophotometry. The enrichment ratio, recovery rate and purity were used as index to optimize the extraction process. The results showed that when the initial concentration of the saponin at 2.0 g/L, the volume at 150 mL, the gas flow rate at 32 L/h, the temperature at 30 ℃ and the solution pH value at 4.3 were used, the enrichment ratio could reach 2.153, and the recovery rate and purity of saponin were up to 79.19 % and 74.68 %, respectively.