Platinum mononuclear complex, cis-[PtCl₂(PyCN)₂] (1, PyCN = 4-cyanopyridine), has been synthesized and characterized by single-crystal X-ray analysis. Compound 1 crystallizes as yellow plates from the reaction of a mixture of K₂PtCl₄ and PyCN (=1:2) in H₂O, that was left to stand at room temperature with the addition of Me₂CO. Compound 1 forms the square-planar coordination geometry around the Pt atom coordinated to two Cl^– ions and two pyridines of PyCN ligands in cis position. Single crystal of 1 shows the temperature dependent phase transition around 140 K, where the crystal space groups change from P2₁/c (high temperature) to (low temperature), which is caused by the stabilization of intermolecular interaction.