By use of synchrotron radiation, powder X-ray diffraction of one-dimensional bis(dimethylglyoximato)nickel(II), Ni(dmg)(2), has been studied at room temperature and at high pressure. The lattice constants with an orthorhombic structure for Ni(dmg)(2) monotonically decrease with increasing pressure up to 7.4 GPa; the linear compressibility of each axis is estimated. The magnitude of the linear compressibility increases in. the order c > b > a in the low-pressure region,. However, the lattice constant along the b-axis is smaller than that along the a-axis at pressures greater than 6GPa. A Ni-Ni distance along the c-axis abruptly decreases from 3.255 angstrom at ambient pressure to 2.82 angstrom at 7.4GPa. A bulk modulus of Ni(dmg)(2) is obtained from the volume versus pressure curve fitted by a Birch equation of state. The bulk modulus of this complex is very small, 8.0 GPa. Ni(dmg)(2) is a very compressible compound. The electrical and optical properties of Ni(dmg)(2) have been investigated at high pressures. The d pi-pi* arid 3d-4p bands shift to a lower energy region with increasing pressure. The absorption peak of the 3d-4p band is very sensitive to pressure. The resistivity of Ni(dmg)(2) decreases monotonically with increasing pressure up to 23GPa. The lowest resistivity of this complex is about 50 Omega cm at around 23 GPa. These electrical and optical properties are closely related to the rapid shrinkage of the Ni-Ni distance with increasing pressure.