Effects of toughening agent and temperature on the free volume and mechanical properties were studied by positron annihilation lifetime spectroscopy（PALS） and dynamic mechanical analysis（DMA） for a serious of epoxy resin samples with different toughening agent content（W/W）.According to the variation of ortho-positronium（o-Ps） lifetime as a function of temperature

the glass transition temperature T

g

and secondary transition temperature T

β

were determined.The introduction of toughening agent markedly affects the structure transition temperature.An interesting phenomenon was found that the toughened sample D2-10（epoxy resin/low viscosity live diluents/10% toughening agent） has a higher T

g

than that of D2-304（epoxy resin/low viscosity live diluents）.This fact indicated that the interfacial interaction between toughening agent and epoxy resin was strengthened with increase of toughening agent content

which can restrain segmental motion

bringing about an increase in T

g

.On the other hand

it’s very interested that the module of compression measured at 233 K is much better than that measured at 303 K

and larger difference of mechanical properties between pure sample and D2-10 sample at low temperature was observed compared with that at high temperature.The effect of free volume

interfacial properties on the mechanical properties was discussed.