We classified 50 receptor units from 10 acupoints supplied by the medium nerve. It was found that the needling stimulation mostly excited slowly adapting receptors and that the classification of acupoint receptors related closely to their location. For example, the Shanyang, Zhongchong, Shaoshang acupoints in the skin needling sensation receptors are touch or pressure receptor units; the receptors of Neiguan, Yuji, etc.; the acupoints located in deep tissue with abundant muscles, are mostly muscle spindles; the Daling acupoint might be a colgi tendon and/or pressure receptor unit. Besides a significant receptor, an acupoint contains one or more needling sensation receptor. The receptors and the afferent fibers of acupoints take part in forming and maintaining the needling sensations.