Myosin was extracted from tilapia (Oreochromis niloti-cus) and the heat-induced gel was prepared, and the effect of CaCl₂ addition on the water holding capacity, microstructure and chemical interactions of myosin gel was investigated under different salt conditions (1,50,150,600 mmol/L NaCl). The effects and mechanisms of Ca²⁺on thermal gel properties of myosin were determined under the low salt conditions. Experimental results showed that under the conditions of low salt concentration (1~150 mmol/L NaCl), there were weak opaque gels due to a rapid aggregation of myosin filaments during heating. These myosin gels exhibited a cross-linked network with coarse cross-linked strands and large cavities, and the water holding capacity of gels was low. Hydrophobic interactions were responsible for the heat-induced gel formation of myosin. During the gelation process, the addition of 10 mmol/L CaCl₂ promoted the unfolding of myosin and caused α-helices to partially turn into β-sheets with the reduced hydrogen bond interactions, thus resulted in stronger disulfide linkages between myosin molecules (P＜0.05), which contributed to the ordered and dense three-dimensional network with significantly improved water holding capacity of myosin gel (P＜0.05). Moreover, this improvement was more obvious at 1 mmol/L NaCl. Therefore, an appropriate amount of CaCl₂ can effectively improve the gel properties of myosin under low salt conditions.