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Ask a mechanical designer, especially those dealing with robotics, what are the two main limitations when designing a new autonomous small mechanism. The answer will most likely be the need for better small-size actuation devices and better and smaller energy sources. Indeed, these two factors impose most of the constraints to designers, reflected in the size of the device, the forces it can apply, its achievable workspace, and the time duration it can work when not connected to a permanent energy source. Usually these parameters are in conflict with each other, that is, a small motor has somewhat low output torque and power, while a motor that can generate a large amount of torque is usually large in size and consumes a lot of power. Consequently, every mechanism designer is eager to design a small actuator that generates a large amount of torque while it simultaneously consumes a reasonable amount of energy. This report explains our efforts in developing an inflatable actuator having a small size yet can apply relatively large torque where at the same time can cover a large workspace. The inflatable actuator is shaped as a bellow which is composed of two materials with different shear modulus—one has high elasticity and the other low. By applying pressure inside the bellow, each of the materials tends to deform according to Hooke’s law, resulting in the bending effect due to the elongation differences between the two materials which are constrained to deform simultaneously. We describe the mechanical concept of the bellow actuator; we also provide an analytical model for the bellow deformation. Experimental results for verification of the model are also presented.