ABSTRACT: In order to elucidate the gelation mechanism of surimi, the temperature dependence of water proton spin–spin relaxation time (1H T2) has been described by a theoretical approach, in which the exposed protein surface is taken into account. Water 1H T2 measured for horse mackerel surimi in the presence of 2.5% NaCl was analyzed on the basis of the consideration for the denaturation and the aggregation of protein in order to explain the macroscopic structural change during the heating and the cooling processes. The temperature dependence of water 1H T2 and the fraction of rigid component gave a clear explanation for the gelation mechanism of surimi. Differential scanning calorimetry thermogram and dynamic viscoelastic measurements supported the results of nuclear magnetic resonance (NMR) measurements. It has been demonstrated that the measurement of NMR relaxation times is useful to describe the gelation mechanism of surimi.