The regular techniques used to incorporate organic and inorganic compounds are experiencing significant expense, not environmental friendly, low proficient and not progressively reasonable in huge scope activities. As of late, we need a productive and eco-friendly manufactured way to deal with blend some significant inorganic or organic compounds in nano scales. Green procedures have the minimization of hurtful synthetic compounds and instrumentations, ease, basic, no unsafe concoction ages and high proficiency. In nano-scale, the capability of the compounds altogether increments and the green synthesis methodologies in engineered science are better other options and effective over customary techniques. In the current investigation, we have synthesized calcium oxide (CaO) nanoparticles by utilizing the leaf extract of Ocimum tenuiflorum. Calcium oxide nanoparticles are discovered important in adsorption, antimicrobial activities, catalysis and absorption. The newly synthesized CaO nanoparticles (CaONP) have been described by various systematic techniques, for example, UV-Visible, DLS, XRD, SEM and EDX. The CaO nanoparticles are pertinent in the antimicrobial activity against gram positive (Bacillus subtilis, Staphylococcus aureus) and gram negative bacteria (Pseudomonas aeruginosa, Escherichia coli) and huge zone of inhibition found over these microorganisms in the following order, S. aureus < B. subtilis < E. coli < P. aeruginosa. CaONP also test for agricultural application as macro nutrient. Plant growth was measured using growth analysis parameters i.e. % germination, relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), leaf weight ratio (LWR), specific leaf area (SLA), specific leaf weight (SLW), leaf area duration (LAD), the physiological response to particular mineral stress calculated by measuring % phytotoxicity, % inhibition, tolerance indices, seed vigor index. The biochemical response to particular CaNP stress calculated by measuring total carbohydrates, total protein, chlorophyll pigment concentrations and peroxidase enzyme activity.