「三歲姑」是「關三姑」儀式活動中被迎請的神靈，又有「椅子姑」或「籃子姑」的別稱。有關「三歲姑」的歌謠，常在民間文學之儀式歌謠的訣術類（含巫術性質）中出現。為了紀念一個被嫂嫂虐待而死的可憐三歲小女孩，女孩們會在元宵夜（或是中秋夜）的時候，準備一些供品、拿一個籃子、再拿一件白衣服、一條烏巾，把籃子打扮成三姑的樣子，再把籃子放在椅子上，之後抬起椅子搖晃，唸起「三歲姑」的歌謠，對三歲姑招魂請靈，希望「三歲姑」的神靈快快降臨或快快上身，除了享受這些祭品之外，也與他們一同玩耍、回應他們的問題，這樣的儀式活動稱為「關三姑」。本文探討的重點，便在論述有關「三歲姑」儀式歌謠和故事傳說的關聯性、歌謠儀式的程序內容，以及其隱含的民俗及文化意義。

This research is to explore and analyze the meaning of 3-year-old gu folk Song, being called "Yi-Zi (chair) Gu", or "Lan-Zi (basket) Gu)", This type of folk song often appears in folk religion in literature that involves with witch character s in Taichung and Chang-Hu areas. The song is to remember a 3-year-old poor girl who was abused by her sister-in-law. On moon Festival Day, there is a folk ceremony to recall the story. In the ceremony the young girl children prepare sacrifices and a basket that is decorated with a white shirt and black towel to make the basket looking like a San Gu. Then they put the San Gu on the chair; and after that they lift it up and down and shake it forward to backward or le ft to right by singing the folk song of 3-year-old gu to expect the spirit of the San Gu comes onto them. Besides, enjoying the sacrificed food, the San Gu also plays with them. This ritual activity is called "Guan (close) San Gu". The focus of this research is to explore this folk story and analyze the relation between the song and story. Also, discuss the procedure of the folk ceremony and its metaphor meanings.