With technological interests in renewable raw materials and more environmentally friendly and sustainable resources, much attention has been focused on cellulose research and application. This paper presents a recent discovery of cellulose papers as smart materials that can be used for bio-mimetic sensor/actuator devices and microelectro-mechanical systems (MEMS). This cellulose paper is termed as Electro-Active paper (EAPap). First, the story of EAPap as an actuation material is addressed along with fabrication and recent improvement of EAPap materials. The actuation mechanism is also explained by gathering all information on physical, chemical, electrical and mechanical observations. Also the functional capability of sensor/actuator is discussed with experimental testimony. The cellulose EAPap materials have merits in terms of ultra-lightweight, dryness, low cost, low actuation voltage, low power consumption and biodegradability. To demonstrate these advantages, applications such as micro insect robots, micro flying objects, MEMS, biosensors and flexible electrical displays are discussed with some examples. In summary, the possibility of cellulose papers as smart materials is addressed with the future direction and challenges in this research.