Samsebul, the altar portrait behind the statue of Buddha in the main building of Bonghwang temple in Andong, has been designated as Tangible Cultural Property No. 406. These alter portraits have significance as the standard of the research of Samsebul in Joseon period. In this study, fibre of the ground textile is identified using microscopic examination, solubility test, ATR-FT-IR, SEM, XRD. Two samples from Yaksabul(A, B), one sample from Seokgabul(C), and one sample from Amitabul(D), which were collected during the conservation process, were prepared for this study. In previous record, above samples were documented as hemp. Due to severe deterioration and accumulated dust layers on these samples, it was hard to recognize them with naked eyes, but through this study, we could identify that all samples except one from Yaksabul(A) are silk.