This study was performed to develop a high reactive epoxy resin system which can be used without heating in winter construction works in cold northern districts.Firstly, the following 3 experiments were conducted.(1) The effect of curing accelerators (66 kinds) on the gelation time of an epoxy resin.(2) The variation in viscosity of the mixtures (24 kinds) of polyepoxide (or hardener)-curing accelerators with a lapse of time.(3) The temperature dependence of viscosity of the mixtures (12 kinds) of polyepoxide (or hardener)-curing accelerators.As a result, it was found that a mixture of hardener-m-cresol has the best quality for practical use with regard to low viscosity, low increase rate of viscosity with lapse of time, low lower limit of usable temperature, and high reactivity.Secondly, 8 kinds of test materials (mixtures of hardener-m-cresol) which have the m-cresol contents ranging from 0 to 140 equivalent per cent at an interval of 20 equivalent per cent were made, and were used for the following 2 experiments.(4) The temperature dependence of viscosity of each test materials.(5) The temperature dependence of gelation time of the mixtures of each test material-polyepoxide.The results obtained from these two experiments were summarized as follows:(1) The test materials which have the m-cresol content below 120 equivalent per cent can be used at the average temperature in January in all cities in Hokkaido with 1 exception.(2) The test materials which have the m-cresol content above 80 equivalent per cent can be used below the freezing point.