Never-dried and dried crab shell chitin and squid pen chitin samples were acid-hydrolyzed in 1 M HCl at 85 degrees C for up to 2 h. The crystallinities, crystal sizes, and degrees of N-acetylation of the acid-hydrolyzed chitin samples are almost unchanged the same before and after acid hydrolysis. The original and acid-hydrolyzed chitin samples were dissolved in 8% (w/w) lithium chloride/N,N,-dimethylacetamide, and the solutions were subjected to size-exclusion chromatography with multiangle laser light scattering analysis to determine their molar masses and molar mass distributions. The molar mass of each chitin sample decreases with increasing acid hydrolysis time, and the weight-average degree of polymerization (DP) becomes constant after acid hydrolysis for 0.5 to 2 h. However, the DP, values of the chitin samples after acid hydrolysis for 2 h (DPI 2h) are different: Never-dried squid pen chitin has the highest DPw-2h of 1530, whereas the DPw-2h values of other chitin samples are in the range 220-410.