Abstract: Disclosed is a leak-proof gel casting device for a vertical protein electrophoresis system which includes a gel caster which has a plurality of compartments and a sealing pad which is inserted to the compartments of the gel cater, and is formed to wrap around both sides and an edge of a lower side of a plate set. The present invention with a simple structure is capable of being manufactured at a low cost, does not require frequent replacement because of its long-term durability, and is highly effective in preventing the leakage of the gel placed in the gap between the plates.