Measurements of ice recrystallization inhibition (IRI) and thermal hysteresis (TH) activities of kappa (κ)‐ and iota (ι)‐carrageenans were carried out to examine whether they can be novel cryoprotectants or not. IRI measurements indicate that both carrageenans reduce recrystallization in sucrose solution, but that the IRI activity of κ‐carregeenan is higher than that of ι‐carrageenan. TH measurements indicate that κ‐ and ι‐carrageenans do not exhibit TH activity. TH activity measurements of antifreeze glycoprotein (AFGP) in the presence of κ‐carregeenan demonstrate that this carregeenan neither influences the TH activity of AFGP nor the shape of the ice crystals. The round ice crystal shape transformed into an angular and elongated shape in the presence of both carregeenans.