The mechanical degradation of poly (${alpha}$-methyl styrene) in several mixed solvents (toluene-n-butyl alcohol, toluene-sec-butyl alcohol, toluene-kerosene, toluene-methyl ethyl ketone), from $1^{circ}C to $45^{circ}C$, was studied using the capillary flow method. The velocity constant of scission reaction (k) and the limited degree of polymerization (g) were compared at the same value of [${eta}$] at each temperatures. As results, mechanical degradation of polymer in dilute mixed solutions is affected by composition of solvents around the polymer chains.