Potassium hydrogen bis-dichloroacetate (1) was synthesized and separated as crystals. Differential scanning calorimetry (DSC) measurement reveals that this compound undergoes a reversible phase transition at about 259 K with a heat hysteresis of 23.5 K. Dielectric anomaly observed at 260 K in the heating process further confirms the phase transition. The room temperature X-ray single-crystal structure determination indicates that 1 crystallizes in the monoclinic crystal system with a centrosymmetric space group P21/c, and cell parameters are a = 6.240(1), b = 23.177(4), c = 7.335(1) Å, β = 106.938(1)°, V = 1014.8(3) Å3, and Z = 4. In the low temperature phase, 1 also crystallizes in monolinic with space group P21/c, and cell parameters are a = 6.180(1), b = 22.988(2), c = 7.200(1) Å, β = 108.098(1)°, V = 972.4(1) Å3, and Z = 4. The structural phase transition is dominating caused by the torsion of bond angles.