Heterocyclic compounds constitute the largest family of organic compounds, regardless of structure and functionality. Heterocyclic compound are of particular interest in medicinal chemistry and this has catalyzed the discovery and development of many new heterocyclic compounds. The compound bearing thiazole and oxazole moiety have been found to possess antimicrobial, antitubercular and anti-inflammatory activity. Benzimidazole derivatives of 3,4-diaminobenzoic acid derivative (IV a, b), have been synthesized which are tautomer of each other, after the synthesis of 4-isothiocyanato-3-methylbutanal (CIT), a reagent. All the synthesized derivatives have been screened with various bacterial and fungal strains viz. Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, Bacillus typhi, Candida albicans, Penicillium chrysogenum, Saccharomyces cerevisiae, Penicillium chrysogenum, Aspergillus niger. After the antimicrobial studies, it were found that compound (IV)a can be act as a standard drug against fungal strain Candida albicans, Sacharomyces cerevisiae, as it showed more inhibition zone than the standard drug Ketoconazole respectively. Compound (IV ) a showed very good activity against fungal strains Aspergillus niger and Penicillium chrysogenum as these derivatives showed comparable inhibition zone than the standard drug Ketoconazole. Thus these compounds can be used as a standard drug having fewer side effects.