NOVELTY - Preparation (M1) of N,N-dimethylacetamide adduct of cefoperazone acid (I), involves: i) reacting 7-amino-3-(5-(1-methyl-1,2,3,4-tetrazolyl)thiomethyl)- Delta 3-cephem-4-carboxylic acid (VI) with amine in suitable solvent; ii) condensing amine salt of (VI) with D(-)- alpha -(4-ethyl-2,3-dioxo-1-piperazinecarboxamido)- alpha -(4-hydroxyphenyl) acetyl chloride (V) in mixture of N,N-dimethylacetamide and solvent; iii) adding water to the reaction mixture; iv) separating organic layer from solution; v) concentrating organic layer; vi) adding alcohol to residue of step v); and vii) isolating (I).    USE - For preparation of N,N-dimethylacetamide adduct of cefoperazone acid; or for preparation of cefoperazone acid or cefoperazone sodium (claimed) used as an antibiotic.    ADVANTAGE - The process provides an efficient and improved process for the preparation of highly pure cefoperazone which is simple, cost-effective, commercially viable, sustainable, eco-friendly, and avoid multiple steps; prepares N,N-dimethylacetamide adduct of cefoperazone acid (I) which is simple, economical, user-friendly and commercially viable; prepares N,N-dimethylacetamide adduct of cefoperazone acid (I) with high purity which can be advantageously used in the preparation of cefoperazone with high purity substantially free of impurities; and prepares N,N-dimethylacetamide adduct of cefoperazone acid (I) which would be easy to implement on commercial scale, avoid excessive use of reagents and organic solvents, and avoid hazardous and risky solvents, thus makes the process more safe.    DETAILED DESCRIPTION - Preparation (M1) of N,N-dimethylacetamide adduct of cefoperazone acid (I), involves: i) reacting the 7-amino-3-(5-(1-methyl-1,2,3,4-tetrazolyl)thiomethyl)- Delta 3-cephem-4-carboxylic acid (VI) with an amine in a suitable solvent; ii) condensing amine salt of (VI) with D(-)- alpha -(4-ethyl-2,3-dioxo-1-piperazinecarboxamido)- alpha -(4-hydroxyphenyl) acetyl chloride (V) in a mixture of N,N-dimethylacetamide and a suitable solvent; iii) adding water to the reaction mixture of step ii); iv) separating the organic layer from solution of step iii); v) concentrating the organic layer of step iv); vi) adding alcohol to the residue of step v) at a suitable temperature; and vii) isolating N,N-dimethylacetamide adduct of cefoperazone (I). An INDEPENDENT CLAIM is included for preparation (M2) of cefoperazone acid (II) or cefoperazone sodium (III), involving: ia) reacting the compound (VI) with an amine in a suitable solvent; iia) condensing amine salt of (VI) of step ia) with the compound (V) in a mixture of N,N-dimethylacetamide and a suitable solvent; iiia) adding water to the reaction mixture of step iia); iva) separating the organic layer from solution of step iiia); va) concentrating the organic layer of step iva); via) adding alcohol to the residue of step va) at a suitable temperature; viia) isolating N,N-dimethylacetamide adduct of cefoperazone acid (I); and viiia) converting N,N-dimethylacetamide adduct of cefoperazone (I) of step viia) to cefoperazone acid (II) or cefoperazone sodium (III).