As the investigation for sustainable aquafeed ingredients intensifies, alternative ingredients such as shellfish waste, fungi, and insects have received increasing attention. Despite the moderate to high protein content in these raw materials, chitin might potentially limit their applications in fish feed. In this study, we investigated the effect of dietary chitin on nutrient digestibility in juvenile rainbow trout (Oncorhynchus mykiss). Trout were acclimated for two weeks followed by a two-week digestibility period. Triplicate groups of trout were fed either a control diet or a control diet where 1.0, 2.5, or 5.0% of wheat meal was replaced by a commercial grade chitin powder from shrimp shells. It was found that the feed conversion ratio gradually increased with increasing dietary chitin inclusion levels. The apparent digestibility of dry matter, organic matter, protein, lipid, and energy showed a strong linear negative correlation to dietary chitin inclusion levels . These findings suggest that even at dietary inclusion levels as low as 1%, chitin exerts adverse effects on both fish performance and nutrient digestibility.