A composite gel with sugar sustained-releasing property, specific designed for endurance athletes during high-intensity and long-duration competitions, was developed and its physicochemical properties and in vitro releasing behavior were evaluated as well. Sodium alginate (NaA) combined with maltodextrin (DE10) were used to prepare the gel matrix, which allowed to carry out high amounts of glucose and fructose to meet the requirements of at least 30g of sugar per hour for 2-3 hours. The appearance and texture of the gel made with 1% NaA and 5 mM glucono delta-lactone (GDL) were superior for other gel formulations. The addition of maltodextrin in NaA gel significantly improved the sustained-releasing effect of the composite gel, while the transparency decreased and hardness increased with increasing the amount of maltodextrin and storage time because of starch retrogradation. Although sugar-releasing behavior became slightly less stable after 1-month storage, adding high amount of DE 10 did closely meet the required sugar-releasing behavior in the first two hours. Subsequently, the sugars were continuously released due to the maltomextrins digestion through the hydrolysis of pancreatic amylases in simulated intestinal fluid to maintain the sugar level. For commercial purposes, a stable gel with good tasting characteristics and control-releasing function for a reasonable shelf-life (6 months) are critically important. Thus, the composite gel was prepared by adjusting pH to meet the low-acid food regulation by using malic acid. As a result, a composite gel made with 0.48% NaA and 22% DE 10 containing 30% sugars (glucose:fructose=2:1) with 5 mM GDL as coagulant under 14mM of malic acid solution are suitable for energy gel preparation for endurance athletes, who may consume it before competition then a stable blood glucose level can be maintained during the early stage of racing.