The present study reflected on high-priority biological activities of novel silver nanoparticles (AgNPs) synthesized via two cold-tolerant strains; namely,Streptomycessp.OSIP1 andStreptomycessp.OSNP14. These AgNPs were synthesized through a green method using culture supernatant of bacteria at 20 degrees C and characterized by several instrumental techniques. The TEM results revealed that the NPs obtained from OSIP1 were smaller (8 nm, average) than those taken from OSIP14 (15 nm, average). Both AgNPs-OSP1 and AgNPs-OSNP14 also posed the strongest growth inhibitory effect against several pathogenic bacteria alone and especially in combination with antibiotics. Smaller NPs especially at 3.9-31.25 mu g/ml concentrations were assumed more effective biofilm inhibitors ofPseudomonas aeruginosa. Cytotoxic activity of both AgNPs (at 25 and 50 mu g/mL concentrations) on mouse colorectal carcinoma cells (CT26) were then studied using methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay. The findings demonstrated that smaller AgNPs at a 50 mu g/mL concentration had 7% more cytotoxicity effects. In conclusion; although AgNPs produced by diverse strains of cold-adaptedStreptomyceshad close characteristics and biological activities, they showed some multifarious properties.