The synthesis and characterization of a series of square planar Pt(II) complexes, which are luminescent at room temperature, are reported. The complexes have the general structure of (C^N)Pt(O^O), where HC^N is 3-phenylpyridazine (ppdz), 3-(4’-biphenyl)pyridazine (4’phppdz), 3-(2’-naphthyl)pyridazine (2’napdz), or 3-(1’-naphthyl)pyridazine (1’napdz), and HO^O is acetylacetone (Hacac). The reaction of K2PtCl4 with HC^N forms the chloro-bridged dimer, (C^N)Pt( µ-Cl)2Pt(C^N), which are cleaved with an ancillary ligand to give the corresponding monomeric (C^N)Pt(O^O) complexes. The emission bands of these complexes are governed by the structure of the cyclometalating ligands, with emission band (lem) ranging from 516 to 645 nm. The two emission bands at (515 and 550 nm) of (ppdz)Pt(acac) complex have 7 and 6 ms of life time which imply those bands are due to phosphorescence decay. The conjugating ring on the pyridazine makes the emission more red shifted which is expected based on molecular orbital calculation. In addition to the alteration of cyclometalating ligands, ancillary ligands also change. These results can be compared with the corresponding Ir(III) complexes.