Disclosed are a transparent thermoplastic resin composition and a molded article prepared therefrom. More particularly, disclosed are a transparent thermoplastic resin composition comprising A) 100 parts by weight of a rubber-reinforced thermoplastic transparent resin, and B) 0.01 to 2 parts by weight of a dihydrocarbyl pentaerythritol diphosphite wherein the A) rubber-reinforced thermoplastic transparent resin is prepared by polymerizing 5 to 60% by weight of a conjugated diene rubber, 20 to 70% by weight of a methacrylic acid alkyl ester monomer or an acrylic acid alkyl ester monomer, 8 to 50% by weight of an aromatic vinyl monomer and 0 to 20% by weight of a vinyl cyanide monomer, and a molded article prepared therefrom. Advantageously, provided are a transparent thermoplastic resin composition which exhibits superior transparency, impact strength and processability and in particular, does not discolor even during long-term storage and does not discolor at 40 to 80 DEG C., which is the condition of container transportation in the summer, and a molded article prepared therefrom.