A storage box having an upper cover, a lower cover pivotally connected with the upper cover and a resilient sealing ring securely received in an edge of the lower cover so as that when the upper cover and the lower cover are engaged with each other, a water-tight engagement is achieved. Furthermore, due to an arcuate front face formed on the upper cover, the engaging force of the upper cover to the lower cover will be enhanced due to the stress-deformation effect.