The surge in seafood consumption worldwide generates abundant by-products that can be efficiently converted into value-added products following circular bioeconomy principles. Squid pens are a rich source of β-chitin, yet conventional extraction relies on harsh chemicals. Deep eutectic solvents (DESs) offer a sustainable alternative to traditional strong acids and bases due to their biodegradability, low toxicity, and recyclability. In this study, eight DES systems based on choline chloride, potassium salts, glycerol, organic acids, and urea were evaluated for the deproteinization of squid pens. The squid pens were treated with different DESs at molar ratio of 1:2 with a solid loading of 5%, w/w, and incubated in a shaking water bath at 80 ^oC for 2 h. Among them, potassium carbonate: glycerol (PCG), choline chloride: urea (CCU), and choline chloride: acetic acid (CCAA) showed the maximum deproteinization efficiencies of 42.47%, 24.83% and 14.16%, respectively. Optimization of DES molar ratios revealed that PCG at a 1:8 molar ratio achieved a maximum yield 36.74% and deproteinization efficiency of 92.41%; CCU at a 1:8 molar ratio achieved a maximum yield 72.66% and deproteinization efficiency of 90.52%; CCAA at a 1:10 molar ratio achieved a maximum yield 52.68% and deproteinization efficiency of 91.31%. The recyclability of DES was also tested and the extracted chitins were analyzed using FTIR, XRD, and SEM. This approach demonstrates an eco-friendly and efficient route to valorize squid pen waste for high-purity chitin extraction with potential applications in food, health, and cosmetics.