The past 10 years has witnessed a renewed interest in cellulose research and application, sparked mostly by technological interests in renewable raw materials and more environmentally friendly and sustainable resources. In this paper, we further expand the current knowledge in cellulose applications and technologies by reporting our discovery of cellulose as a smart material that can be used for biomimetic sensor/actuator devices and micro-electromechanical systems. This smart cellulose is termed electroactive paper (EAPap). It can produce a large bending displacement with low actuation voltage and low power consumption. The actuation phenomenon and its characteristics are illustrated in this paper. Because cellulose EAPap is ultra-lightweight, inexpensive, and biodegradable, it is advantageous for many applications such as micro-insect robots, micro-flying objects, micro-electromechanical systems, biosensors, and flexible electrical displays.