A retractable lens assembly with a variable-volume lens is provided. The retractable lens assembly includes an optical lens, a variable-volume lens, a fluid pump, a communication tube, and a storage tank. The variable-volume lens includes a lens film, an accommodation space wrapped by the lens film, and a transparent fluid within the accommodation space. Therefore, when the transparent fluid is pumped from the accommodation space to the storage tank by the fluid pump, the variable-volume lens is folded because of atmospheric pressure, such that the overall thickness and volume are reduced. When the variable-volume lens is folded, the thickness of the retractable lens assembly is as small as possible. When the variable-volume lens is stretched out because of being filled with the transparent fluid, the variable-volume lens and the optical lens are of a coaxial configuration, forming a photographic optical system.