Novel acyl pyrazolone and thio-Schiff base of acyl pyrazolone ligand HL (2-((4-chlorophenyl)(1-(3-chlorophenyl)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazol-4-yl)methylene) hydrazine-1-carbothioamide) has been synthesised and characterized by FT-IR and 1H NMR techniques. This unusual coordinated complex [Zn(L)(CH3C00)(H2O)]CH3CH2OH has been synthesized and characterized by FT-IR, thermogravimetric analysis (TGA), UV-Vis spectroscopy and single crystal X-ray diffraction. 1H NMR confirms the structure of the thio-Schiff base used in the study. The structural data reveal that mononuclear Zn(II)complex has distorted square pyramidal geometry. S-S interaction, Inter molecular and intra molecular H-Bond found in crystal packing of the complex. The complex has been screened for MTT assay against A549 cell lines. The Zn(II) complex is cytotoxic against the screened cell line at low concentration.