This work aims to evaluate biol. activities and toxicity of copper nanoparticles (CuNPs) synthesized from Perilla frutescens (Linn.) Britt leaves extract Microscopic techniques showed the poly dispersed CuNPs with a size of 30-65 nm and high resolution X-ray diffraction (HR-XRD) revealed the fcc. Cu. CuNPs significantly inhibited the growth of few human pathogenic bacteria namely, Staphylococcus aureus, Escherichia coli, Salmonella typhimurium and Bacillus cereus and a fungal pathogen, Alternaria alternata at 40μg/40μl concentration Mode of action of CuNPs against the bacterial pathogens was demonstrated using biol. transmission electron microscope (Bio-TEM). >60% inhibition was observed against MCF-7 cells at 160μg/mL of CuNPs and the apoptotic morphol. was confirmed using ethidium homodimer and casein staining. Finally, the toxicity of CuNPs was studied using zebrafish embryo and higher toxic effects were recorded even at 1.5μg/mL of CuNPs. Therefore, the toxicity of CuNPs must be thoroughly studied.