In order to obtain epoxy based composite with low coefficient of thermal expansion (CTE) and good mechanical properties at cryogenic temperature (77 K), core–shell rubber (CSR) particles were integrated into epoxy. Fourier transform infrared spectroscopy results showed the occurrence of intermolecular hydrogen bond between the CSR particles and the epoxy matrix. The results of thermomechanical analysis indicate that the CTE of CSR–epoxy composites below Tg reached the minimum of the CSR content of 0·5 wt-%, then followed by an increase when the CSR content was higher than 0·5 wt-%. The CTE value under Tg was decreased 18·89% with 0·5 wt-% CSR content. The tensile strength, Young's modulus and impact strength of CSR–epoxy composites at 77 K all reached a maximum with the CSR content of 0·5 wt-%, followed by a decrease when the CSR content was higher than 0·5 wt-%. The storage modulus of CSR modified epoxy resin in glassy region was higher than that of the neat epoxy resin.