This study examines “a transformation painting of Maitreya Sangsengkyung <彌勒上生經變相圖>,” which is portrayed in the shrine E204 in a temple known as Xidasi in Beiting, north of Turfan. Specifically, this study deals with the interpretation of the iconographies in the painting and its production background. Except for brief reports on its present condition, no study is found regarding “a transformation painting of Maitreya Sangsengkyung” in Xidasi. There seem to be a couple of reasons: first, this painting is unique and different from other Maitreya-related transformation paintings. Second, its geographical location is not easily accessible. Third, it is seriously damaged and that makes it difficult to be recognized without careful observation. This wall painting in Xidasi consists of four paintings and describes the story of ‘Sangsengkyung 『上生經』’ in the order of from bottom to top. In detail, the first painting, i.e. the bottom one, depicts that Noedobalje(牢度跋提) offers a prayer and that Tusita-deva(兜率天宮) will be made by fifty trillion(五百萬億) heavenly beings offering consecrated crowns. The second painting, from the bottom, illustrates five heavenly gods, with Jungeumsung(正音聲) at the center, decorating Tusita-deva and a heavenly maiden being born in a lotus flower on a stream of treasure. The third painting portrays Bumwang(梵王) on every side, offering treasures, and fifty billion Bonyu(寶女). The forth painting, i.e. the one at the top, represents Maitreya- bodhisattva sitting in the lotus position on a lotus pedestal. This fully illustrates the story of ‘Sangsengkyung’, and that identifies this painting as “a transformation painting of Maitreya Sangsengkyung”. To estimate the age in which this painting was produced, its counterparts were used as references. They are “a transformation painting of Maitreya Sangsengkyung” of Xixia(西夏) dynasty, painted in WanFudong(萬佛洞) in Mountain of Wenshu(文殊山), “a woodcut print of Gwan Maitreya-bodhisattva Sangseng Tusita-deva Scripture <觀彌勒菩薩上生兜率天經板本>” painted in the year 1189, and paintings in Bezeklik(栢孜克里克) caves. Before this investigation was conducted, the age in which “a transformation painting of Maitreya Sangsengkyung” in Xidasi was produced was commonly thought to be between the mid 10th and the late 13th century. However, this investigation narrowed down its age to between the mid 10th and the early 12th century. Even though Maitreya Buddhism declined in China after the 9th century, there seem to be explanations of how “a transformation painting of Maitreya Sangsengkyung” was painted in Xidasi, Beiting, which used to be a summer palace of west Uighur. And that is the fact that ‘Sangsengkyung’ is an apocrypha, compiled in Turfan. In addition, regardless of its decline in the Chinese mainland, Maitreya Buddhism was kept in Turfan through its union and development together with Manichaeism. Maitreya-related scriptures in Uighur and such documents found in Turfan are provided as evidence. Apart from the fact that “a transformation painting of Maitreya Sangsengkyung” in Xidasi was produced in Turfan, where ‘Sangsengkyung’ was compiled, and that it describes the story of ‘Sangsengkyung’ thoroughly, it also shows its regional characteristics clearly, with iconographies and composition different from China and Dunhuang(敦煌). In addition, this painting seems to have been passed on to Xixia- in WanFudong in Mountain of Wenshu- by monks visiting and by the exchange of Buddhist scriptures, and it suggests an exchange between west Uighur and Xixia.