Because sensor's and electrical techniques is progressing, some physiological instruments, like pulse oximeter oxygen saturation, electrocardiograph, body temperature, and heart rate monitor, have been developed as the wearable apparatuses. Now, the electrical blood pressure monitor all uses a cuff to measure the blood pressure. If the electrical blood pressure monitor wants to become a wearable apparatus, it has to develop the cuffless technique. The goal of this study is to develop an impedance-plethysmography technique for the cuffless blood pressure measurement. In this study, we designed an impedance-plethysmography ring to measure the impedance-plethysmography signal. The electrocardiography and photo-plethysmography signals also were measured in the same time to get the pulse transit time which was used to estimate the blood pressure. Twenty healthy subjects participated in this study. The results showed that the change of systolic pressure had a better relation with the change of the pulse transit time by impedance-plethysmography technique than pulse transit time by photo-plethysmography technique (r=0.700 vs r=0.450).