An abnormal male adult of an ambush bug species, Amblythyreus potaninae (Bianchi, 1899), from Yunnan Province of China is described. Antennae are asymmetrical with right antenna 2-segmented and left antenna 3-segmented (4-segmented in normal). Rostrum one-segmented (3-segmented in normal). Pronotum is slightly asymmetrical with left anterior angle rounded and right anterior acutely pointed. Right protibia is about 4/5 of normal in length. Right meso- and metatibiae curved and about 1/3 length of normal, with tarsi and pretarsi absent. All deformed parts of A. potaninae are illustrated and the scanning electron microscopic photos of the abnormal and normal left antennae are provided.