The seed yield of summer plants is affected by climate change due to high temperature. High temperature during the reproductive growth period decrease pod, seed weight in soybean. This study was conducted at National Institute of Crop Science (NICS) during the growing season. The objective of this study was to determine the effect of high temperature on growth and seed yield responses of soybean varieties using a temperature gradient chamber (TGC). In 2017, the Daewonkong (DWK), Pungsannamulkong (PSNK), and Deapungkong (DPK) were grown in three TGCs. Four temperature treatments, Ta (near ambient temperature), Ta+1 (ambient temperature+1℃), Ta+2℃ (ambient temperature+2℃), Ta+3℃ (ambient temperature+3℃), Ta+4℃ (ambient temperature+4℃), were established by dividing the rows along which the temperature gradient was created. In all three cultivars, beginning bloom (R1) delayed at elevated temperature in Ta+4℃. In addition, the days to beginning of seed fill and maturity were longer under higher temperature. The numbers of pod, 100 seed weight, and seed yield increased at elevated temperature in DWK. In contrast, seed yield components of PSNK and DPK were reduced in Ta+4℃. The results suggest that 100 seed weight and seed size of soybean was low by increased temperature in Ta+4℃ of PSNK and DPK.