We have previously reported that high-temperature (42°C) culture inhibited the proliferation of human umbilical endothelial cells (HUVECs). We described how the proliferative capacity and telomere length (TL)-related parameters of HUVECs, one of somatic cells, change with culture temperature. It was speculated that a combination of cytostatic manipulations, such as anticancer treatments, and high-temperature conditions would more effectively suppress the growth of somatic cells. Therefore, we hypothesized that increasing the core body temperature (BT) as a pretreatment for cancer treatment enhances the effectiveness of cancer treatment. In the present study, various cells (HUVECs, Jurkat cells, and SLVL) were cultured under different temperature conditions (35°C, 37°C or 39°C) combined with anticancer manipulations (X-ray irradiation or addition of 1-β-D-Arabinofuranosylcytosine [Ara-C]), which resulted in changes in the proliferation rate and TL. The degree of cell proliferation inhibitory effect depended on the combination of cell type, anticancer procedure, and temperature condition. Therefore, the best therapeutic condition might be selected in advance by checking the proliferation rate of biopsied cancer cells being cultured under combinations of anticancer manipulations at altered temperature conditions.