The study was carried out to determine relative protein digestibility (RPD) of different feed ingredients for Thai koi (Anabas. testudineus; n=22) using in vitro digestibility technique. Gut crude enzyme extracted from the experimental species was used to assay RPD using pH drop method. The RPD of fish meal (FM), meat & bone meal (M&B), shrimp meal (SM), soybean meal (SM), mustard oilcake (MOC) and rice polish (RP) were 78.08%, 72.82%, 20.65%, 76.08%, 67.39% and 35.86%, respectively when the respective ingredients were hydrolyzed by the gut crude enzyme extract of A. testudineus and caesin was used as the standard. The highest relative protein digestibility was found in fish meal (78.08 %) and the lowest was found in shrimp meal (35.65 %). The determined RPD of different feed ingredients can be used as the base information for the feed preparation of A. testudineus.