The curing reaction of bisphenol S epoxy resin (BPSER) with 4,4'-diaminodiphenylmethane (DDM) was studied by means of torsional braid analysis (TBA) in the temperature range of 393-433 K. The glass transition temperature (T-g) of the BPSER/DDM system is determined, and the results show that the reaction rate increases with increasing the T-g in terms of the rate constant, but decreases with increasing conversion.(1) The T-g of BPSER/DDM is about 40 K higher than BPAER/DDM. The gelation and vitrification time were assigned by the isothermal TEA under 373 K; in addition, an FTIR spectrum was carried out to describe the change of the molecular structure. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of the BPSER/DDM has n-order reaction kinetics.(2)