A styrene resin composition is provided which has a high molecular weight enabling a molded product obtained therefrom to have satisfactory strength, has a high melt mass-flow rate, high melt tension, and hence excellent moldability, and is less apt to gel during production, and a process for producing such a styrene resin composition. The styrene resin composition comprises a linear polystyrene having a weight average molecular weight of 200,000 to 350,000 and a multibranched polystyrene having a weight average molecular weight of 1,000,000 to 10,000,000, has an average molecular weight of 250,000 to 700,000, and a melt mass-flow rate (MFR) and melt tension (MT) which satisfy the following formulas (1) and (2) respectively:

MFR45exp(-0.1Mw10^-4)  (1)

MT0.07Mw10^-4+1.8.  (2)