Heng-ch'un area, a peninsula in southern Taiwan,is divided into five towns, and the inhabitants consist of aborigines(Paiwan, Puyuma, Ami and Makatao people), Chinese immigrants (Fukien and Hak-ka people), and aborigine-immigrant mixed people. Folksongs popular in Heng-ch'un area are referred to as Heng-ch'un Diao (the tunes of Heng-ch'un) and consist of five tunes, including Su-hsiang-ch'i, su-chi-ch'un, Wu-k'ung'hsiao-diao,P'ing-p'u-diao,and Niu-wei pai. Heng-ch'un folksongs mostly relate to love or morality, and the lyrics may be performed in a quatrain form which has seven monosyllabic Chinese characters in each line, or in an irregular-character distich form; however, the latter is only used in the tune Niu-wei-pai. Based on the verse form, performers can improvise lyrics. These songs usually follow a strophic structure, but the melody of each strophe often changes according to the tones of the different lyrics. The main purpose of this article is to discuss the skeleton of Heng-ch'un folksongs, and factors, specifically linguistic features, that make melody vary. The skeleton of each tune is unchangeable and unique, and mainly consist of its characteristic melodic patterns and the fixed interval relationship between ending tones of lines in each stanza. And, the factors in respects of language, aesthetic, and individual background would make performers produce greatly varied melodies based on limited tunes.