The electrical properties of plants represent physiological activities including water and ion transport in their stems. Therefore, monitoring electrical conductivity in plants (ECp) can be used to detect plant responses to changes in environmental conditions. Stable measurement of internal ECp was developed to evaluate the relationship between the ECp and environmental factors. Two electrodes with three needles were inserted into each side of paprika stems to monitor paprika ECp in response to the environmental factors of temperature, irradiation, and relative humidity. The ECp was positively correlated with irradiation and temperature (R2 = 0.642 and 0.815, respectively), but negatively correlated with relative humidity (R2 = -0.416). The ECp was higher in May than in February due to size differences in the vascular bundle sheaths as well as changes in irradiation and temperature. The ECp was predicted using a regression equation that described environmental data, and the predicted results corresponded well to plant measurements. The ECp was higher during the day than at night, which was attributed to higher daytime water content in the stems.