INTRODUCTIONChalcones (1) and pyrazoles (2) are the most important classes of flavonoids and alkaloids respectively present across the whole plant kingdom [1,2]. Both have interesting bioactive features associated with several biological activities. Chalcones and their derivatives demonstrate wide range of biological activities such as antidiabetic, antineoplastic, antihypertensive, antiretroviral, anti-inflammatory [3], antiparasitic [4], antihistaminic [5], antimalarial [6], antioxidant [7], antifungal [8], antiobesity [9], antiplatelet [10], antitubercular [11], immunosuppressant [12] etc. Also, pyrazole nucleus has found considerable attention due to its potent medicinal scaffolds and exhibits full spectrum of biological activities. Many pyrazole derivatives have already found their application as antimicrobial [13-16], antifungal [17], anticancer [18-20], anti-inflammatory [13,21-26], antiviral [14], antioxidant [27], etc.Chalcone is an acyclic compound with substituted aromatic ring at both side of the double bond which allows the molecule to adopt many conformations due to weak π-π interactions A series of 16 chalcone compounds were synthesized by Claisen-Schmidt condensation of various aldehydes with acetophenone using KOH as a base in ethanol. The reaction affords the desired products in good yields. Then all the 16 compounds were converted into pyrazoles by treating with hydrazine hydrate in ethanol under reflux condition. Both chalcones and pyrazoles were screened for their in vitro antibacterial (Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa) and antifungal (Aspergillus flavus, Chrysosporium keratinophilum and Candida albicans) activity. Biological activities of these compounds were compared with those of commercially available antibiotic ampicillin and antifungal agent miconazole. Pyrazoles were found to be most active and effective than corresponding chalcones for antimicrobial activity. Out of the 7 pyrazole compounds tested for antibacterial and antifungal activity, 5 compounds, 4h, 4j, 4l, 4m and 4n are turned out to be potent antimicrobial agents. Therefore these derivatives could serve as a highly promising molecules for further development.