In this work, the tunicate cellulose nanocrystal (tCNC) was extracted from tunicate by bleaching and acid hydrolysis. It was used as ller in the preparation of sodium alginate-based enteric capsule. The addition of tCNC with high aspect ratio (65) rendered the enteric capsule excellent physical properties. Compared with the control sample, when the addition of tCNC was 10% (wt), the water contact angle of the capsule was enhanced by 46.0%, the opacity was increased by 356.8%, the maximum tensile stress was increased by 142.6%, the modulus of elasticity was increased by 240.3%, and the elongation at break was increased by 133.8%. In the in vitro degradation experiments, the capsule hardly degraded in the gastric environment (pH 1.2), while in the intestinal environment (pH 6.8), the degradation became slower with the increase of tCNC content, which was consistent with the properties of enteric capsule. This research developed a new direction for the application of tCNC in the pharmaceutical material productions.