Nisyros is a poorly known Quarternary volcano, south-east of the Agean volcanic arc. It is characterized by periods of intense seismic activity and paucity in reruptive episodes, sometimes accompanied by hydrothermal explosions. The most recent unrest episode lasted from 1995 to 1998, without eruption. Radar interferometry has been applied in order to study the evolution of the deformation from 1995 to 2000. Observations show a continuous uplift of 140mm during 1995-1997. At mid 1998, the movement trend changes into a slower surface deflation til 2000. Maximum crust deformation is constantly observed at the north-west part of the island, where most earthquake epicenters are located and in agreement to three GPS campaigns conducted between mid 1997 and mid 1998. We solve for the best-fit Mogi point source and best-fit Okada rectangular dislocation of the observed deformation field. Mogi model indicates a source at 5km depth beneath the north-west edge of the island, with a maximum deformation amplitude at surface of 0.14 plus or minus 0.02m and a total volume change of 26 plus or minus 4 × 106 m3, during 1995-1997. The Okada model indicats a dike solution 2km long, 2.2km wide, wiht a 4m opening and a 30° dip. The upper center is at 6.4km depth and the volume change, also during 1995-1997, is 17.6 × 106 m3. Each solution is discussed on the potential controlling mechanism resulting to the volcano's inflation/deflation sequence.