A process for producing powder, flakes, or pellets containing .alpha.-sulfo fatty acid alkylester salt in high concentrations, the process including: (1) a step of preparing a paste containing .alpha.-sulfo fatty acid alkylester salt; (2) a step of aging the thus obtained paste; (3) a step of making the aged paste into flakes or pellets containing equal to or less than 10 wt % of water and then optionally crushing the resulting flakes or pellets into a powder having an average particle diameter of 100-1500 .mu.m; and (4) a step of aging The powder, flakes, or pellets.