By use of synchrotron radiation, powder x-ray diffraction patterns of the one-dimensional complex bis(1,2-benzoquinonedioximato)platinum(II), Pt(bqd)(2) , have been measured at high pressures. The pressure dependence of the lattice constants with an orthorhombic structure in this complex was studied at room temperature. The c-axis (twice the Pt-Pt distance) decreases monotonically with an increasing pressure of up to 5 GPa at room temperature. However, the a-axis increases abruptly at around 2 GPa; the b-axis decreases rapidly at around this pressure. We have found the anomalous pressure dependence of the lattice parameters above 2 GPa. Ratios of a- and b-axes, a/b for Pt(bqd)(2) , are 2.123 at ambient pressure and 2.434 at 4.4 GPa. The crystal structure of Pt(bqd)(2) becomes more anisotropic at higher pressures. The anomalous structural behavior of Pt(bqd)(2) at high pressure is discussed.