We report iota-carrageenan hydrolysis by Pseudoalteromonas carrageenovora IFO 12985. Kappa-carrageenase and lambda-carrageenase were previously isolated from this organism, but iota-carrageenase activity had not been reported in the literature. P. carrageenovora was grown in iota-carrageenan-based liquid medium. Using the zone of depression assay, transfer of aliquots of the culture to solid medium with 2% iota- and kappa-carrageenan showed extensive hydrolysis of iota-carrageenan. Analysis of the hydrolysates by C-13 Nuclear Magnetic Resonance spectroscopy confirmed degradation of the iota-carrageenan. Hydrolytic activity of P. carrageenovora grown in iota-carrageenan was compared with that of the same organism grown in kappa-carrageenan. Cell-free supernatants from each yielded subtle differences in hydrolytic profiles, but showed degradation patterns consistent with hydrolysis to fragments smaller than 1.4 kDa, corresponding to six or fewer monosaccharide units. Different protein expression bands on SDS-PAGE were also observed for the cell-free supernatants of P. carrageenovora grown in iota- versus kappa-carrageenan, with lower kappa-carrageenase expression observed in the organism grown in iota-carrageenan.