There have been many studies on strain-resistance or piezoresistance e-textile sensors. However, the important and critical factor, i.e., the elongation capability of the sensor against the actual stretching of the skin, has not been addressed yet. In this study, we propose a human joint angle estimation method with e-textile strain-resistance sensors. The stretching of the skin, on which the sensor is attached, is visually analyzed in terms of the stretching capability of the sensor and the actual stretching length of the skin. The overall system platform used to obtain and process the sensor data is described. The proposed system is implemented and applied to the elbow joint of a healthy subject. It was found that the sensors should be attached to the skin properly, especially when the skin is not stretched. It is necessary to consider the stretching capability of the sensor to accommodate the actual stretching of the skin. The two sensors attached on the lateral and medial sides provide complementary information, which can be utilized in a sensor fusion context.