The plant bioelectric potential is believed to be a suitable real-time and noninvasive method that can be used to evaluate plant activities, such as the photosynthetic reaction. The amplitude of the bioelectric potential response when plants are illuminated is correlated with the photosynthetic rate. However, practically, the bioelectric potential is affected by various cultivation parameters. This study analyzes the relationship between the bioelectric potential response and the illuminating parameters using a neural network to improve the accuracy of the photosynthetic rate evaluation. The variation of the illuminating colors to the plant affected the relationship between the amplitude of the bioelectric potential response and the photosynthetic rate; therefore, evaluating the photosynthetic rate using the amplitude is difficult. The analysis result shows that the correlation coefficient between the actual measured photosynthetic rate and the estimated photosynthetic rate by the neural network is 0.95. The photosynthetic rate evaluation using the bioelectric potential response is improved and this correlation coefficient is greater than that analyzed by the neural network using only the illuminating parameters. This result indicates that the information on the plant bioelectric potential response contributed to the accurate estimation of the photosynthetic rate.