This study elaborated a systematic and consistent technique for predicting 1:1 entrainment patterns in two-neuron networks based on the phase resetting curve (PRC). The graphical method of the first-order PRC is intuitive and successfully predicts both the entrained period and the phase difference between neural oscillators. It was found that the shape of the synaptic current is not critical in determining the PRC, but the area of the injected current versus time, which is the exchanged electric charge, is a crucial factor. The PRC-based existence and stability criterion for entrainment is in good agreement with the experimental data.