Shrimp processing by-product is considered a valuable source of bioactive compounds, particularly carotenoids such as astaxanthin. The aim of this study was to investigate the effects of enzymatic hydrolysis and ultrasound treatment on astaxanthin extraction and antioxidant activity of extracts obtained from Jinga shrimp (Metapenaeus affinis) by-product. Astaxanthin extraction was performed using different methods including solvent extraction, enzymatic hydrolysis at different enzyme concentrations (0.5, 1, and 1.5%), and a combination of enzymatic hydrolysis and ultrasound treatment at 100 W. The antioxidant activity of the extracts was evaluated using DPPH and ABTS radical scavenging assays as well as ferric reducing antioxidant power (FRAP) assay. Fourier-transform infrared spectroscopy (FTIR) was also employed to identify the functional groups present in the extracts. The results showed that solvent extraction provided the highest astaxanthin yield, whereas enzymatic and enzymatic–ultrasound treatments exhibited higher antioxidant activity. In the DPPH assay, the 1.5% enzymatic treatment combined with 15 min ultrasound showed the lowest IC₅₀ value, indicating significantly greater radical scavenging activity. Similarly, in both ABTS and FRAP assays, enzymatic–ultrasound treatments demonstrated superior performance compared with the other treatments. FTIR analysis also confirmed the presence of functional groups associated with carotenoid structures. Overall, the combination of enzymatic hydrolysis and ultrasound treatment can be considered an effective approach for enhancing astaxanthin release and improving the antioxidant capacity of extracts derived from shrimp by-product.