A process for producing a highly purified glucosyl stevia composition, comprising the steps of: adding starch into water to form a starch suspension; adding a mixture of α -amylase and CGTase into the starch suspension and incubating for about 0.5 to 2 hours at about 75-80°C, resulting in a first liquefied starch suspension; inactivating the α -amylase by low pH heat treatment; cooling the first liquefied starch suspension and adjusting the pH to about 5.5 to 7.0; adding steviol glycosides into the first liquefied starch suspension, resulting in a first reaction mixture; adding CGTase into the first reaction mixture and incubating for about 12 to 48 hours at about 55-75°C; removing non-reactant maltoologosaccharides by contacting the first reaction mixture with macroporous adsorbent resin and subsequently eluting adsorbed diterpene glycosides with aqueous ethanol to result in a glycosidecontaining first aqueous ethanol eluate; removing ethanol from the first aqueous ethanol eluate, resulting in a first aqueous eluate; concentrating and drying the first aqueous eluate to obtain the first dried glucosyl stevia composition; preparing a second liquefied starch suspension in the same manner as the first liquefied starch suspension; adding the first dried glucosyl stevia composition into the second liquefied starch suspension, resulting in the second reaction mixture; adding CGTase into the second reaction mixture and incubating for about 12 to 48 hours at about 55-75°C; inactivating the enzyme in the second reaction mixture by heat treatment; decolourising the second reaction mixture; removing non-diterpene compounds by contacting the decolourised second reaction mixture with macroporous adsorbent resin and subsequently eluting adsorbed diterpene glycosides with aqueous ethanol to result in a glycoside-containing second aqueous ethanol eluate; desalting the glycoside-containing second aqueous ethanol eluate with ion-exchange resins; removing ethanol from the second aqueous ethanol eluate, resulting in a second aqueous eluate; and concentrating and drying the second aqueous eluate to obtain the highly purified glucosyl stevia composition; wherein the highly purified glucosyl stevia composition comprises steviol glycosides and their derivatives having up to twenty α-1,4-glucosyl residues. adding starch into water to form a starch suspension; adding a mixture of α -amylase and CGTase into the starch suspension and incubating for about 0.5 to 2 hours at about 75-80°C, resulting in a first liquefied starch suspension; inactivating the α -amylase by low pH heat treatment; cooling the first liquefied starch suspension and adjusting the pH to about 5.5 to 7.0; adding steviol glycosides into the first liquefied starch suspension, resulting in a first reaction mixture; adding CGTase into the first reaction mixture and incubating for about 12 to 48 hours at about 55-75°C; removing non-reactant maltoologosaccharides by contacting the first reaction mixture with macroporous adsorbent resin and subsequently eluting adsorbed diterpene glycosides with aqueous ethanol to result in a glycosidecontaining first aqueous ethanol eluate; removing ethanol from the first aqueous ethanol eluate, resulting in a first aqueous eluate; concentrating and drying the first aqueous eluate to obtain the first dried glucosyl stevia composition; preparing a second liquefied starch suspension in the same manner as the first liquefied starch suspension; adding the first dried glucosyl stevia composition into the second liquefied starch suspension, resulting in the second reaction mixture; adding CGTase into the second reaction mixture and incubating for about 12 to 48 hours at about 55-75°C; inactivating the enzyme in the second reaction mixture by heat treatment; decolourising the second reaction mixture; removing non-diterpene compounds by contacting the decolourised second reaction mixture with macroporous adsorbent resin and subsequently eluting adsorbed diterpene glycosides with aqueous ethanol to result in a glycoside-containing second aqueous ethanol eluate; desalting the glycoside-containing second aqueous ethanol eluate with ion-exchange resins; removing ethanol from the second aqueous ethanol eluate, resulting in a second aqueous eluate; and concentrating and drying the second aqueous eluate to obtain the highly purified glucosyl stevia composition; wherein the highly purified glucosyl stevia composition comprises steviol glycosides and their derivatives having up to twenty α-1,4-glucosyl residues.