A series of blends with varies compositions was prepared by melt—mixing on the basis of poly- (phthalazinone ether sulfone ketone)(PPESK)and poly(ether sulfone)(PES)．The thermal stability of PPESK／PES blends was characterized by kinetic studies using dynamic thermogravity in nitrogen atmosphere．The dynamic mechanical properties of blends were carried out with DMTA. The results showed that the thermal degradation displayed a two—step reaction and the degradation of PPESK Was found to be a first order reaction in nitrogen．It suggested that the degradation of PPESK in nitrogen was just related with the material properties not with the rate of temperature increasing．The dynamic data such as the apparent activation energy before 15％ loss mass

Ea of 240 kJ／mol．were analyzed using Ozawa method．The thermal degradation rate of PPESK was slowed with increasing heating rate．Besides

the storage modulus of PPESK decreased a little with temperature increasing before 280℃

however

it had a remark drop in the temperature range of 280℃ to 330 ℃．The presence of PES in PPESK resin reduced the storage modulus and thermal stability．