* Corresponding author: Netra Lal Bhandari (ORCID: 0000-0002-4534-374X)  E-mail: netra.tu.edu@gmail.com  Tel number: 977-9841502699 © 2020 by SPC (Sami Publishing Company) Advanced Journal of Chemistry-Section B Natural Products and Medical Chemistry Journal homepage: http://www.ajchem-b.com/ Original Research Article Study of Phyto- and Physicochemical Analysis, Antimicrobial and Antioxidant Activities of Essential Oil Extract of Callistemon citrinus (Curtis) Skeels Leaves Netra Lal Bhandari* 1 , Sunita Khadka 1,2 , Babu Raj Dhungana 1 , Ganesh Bhandari 1 , Tara Datt Bhatt 2 , Durga Prasad Pandey 3 1Department of Chemistry, Tri-Chandra Multiple Campus, Tribhuvan University, Kathmandu, Nepal 2 Department of Plant Resources, Government of Nepal, Kathmandu, Nepal 3Research Center for Applied Science and Technology (RECAST), Tribhuvan University, Kirtipur, Kathmandu, Nepal A R T I C L E I N F O A B S T R A C T Article history Submitted: 2020-10-27 Revised: 2021-02-06 Accepted: 2021-02-26 Available online: 2021-03-03 Manuscript ID: AJCB-2010-1067 DOI: 10.22034/ajcb.2021.254741.1067 The essential oil was extracted from the leaves of Callistemon citrinus (Bottlebrush) by hydro-distillation using a Clevenger apparatus. The component analysis of the oil was carried out by GC-MS technique, which showed eucalyptol (56.47%), α-pinene (18.80%), and D-limonene (9.91%), as the major compounds in C. citrinus oil. The physicochemical parameters such as yield percentage, specific gravity, refractive index, optical rotation, acid value, saponification value, and ester value were determined. The antioxidant activities of extracting oils were determined by DPPH assay and the radical scavenging activity (IC50) value was calculated. The remarkable free radical scavenging effect was observed in bottlebrush oil with IC50 = 390.73 µg/mL. Bottlebrush oil (50% and 100%) exhibited antimicrobial activity against all the four selected strains of bacteria (E. coli, S. aureus, B. subtilis, S. dysenteriae) as well as fungi (Candida albicans). K E Y W O R D S C. citrinus, GC-MS, Antioxidant activity, DPPH assay, Antimicrobial activity Advanced Journal of Chemistry, Section B, 2021, 3(2), 109-119