A crystalline alpha-maltose with an alpha-maltose isomer content of 55% or higher is prepared by the process comprising preparing a high-concentration syrup, with a moisture content lower than 10 w/w %, from a high-purity maltose with a maltose content of 85% or higher; crystallizing alpha-maltose from the syrup at a temperature within the range of 50.degree.-130.degree. C. in the presence of seed crystal; and recovering the resultant crystalline alpha-maltose with an alpha-maltose isomer content of 55% or higher. The crystalline alpha-maltose is superior to crystalline beta-maltose hydrate in solubility and dispersibility in aqueous media. The crystalline alpha-maltose is a suitable maltose material for food products and pharmaceuticals. A ready-mix-type parenteral hyperalimentation which is highly resistant to browning and alteration is prepared with the crystalline alpha-maltose.