Mastitis in dairy cattle is one of the most frequently diagnosed diseases worldwide. The chief etiological agents of mastitis are bacteria of the genus Streptococcus spp. Streptococci are frequently isolated from bovine mastitis in dairy cows . Antibiotics used to treat bacterial infections can become ineffective over time due to emergence of antibiotic resistant pathogens, with the advent of nanotechnology, silver nanoparticles (AgNPs) have gained significant attention as a therapeutic agent due to the well-known antimicrobial properties of silver. the aim of our study was to show an In vitro investigation of the efficacy of some antibacterial drugs against streptococcus isolated from mastitis in dairy cattle and also to show the effect of AgNPs and AgNPs -loaded penicillin on that isolate. In the current study, Antibiotic resistance profiles in streptococcus spp. and resistance genes against penicillin and gentamycin was detected for Pbp1A target gene and aac (6') aph (2'') target gene, respectively, penicillin was loaded onto AgNPs, thus enhancing penicillin antibacterial activity against streptococci. The prepared AgNPs and their conjugates were characterized by Transmission electron microscopy (TEM) and Zeta potential analysis. The minimum inhibitory concentration (MIC) of AgNPs and their conjugates were also determined. The results explained that the lowest concentration that inhibited the growth of streptococcus spp. was 50 PPM for AgNPs, while 12.5 PPM for AgNPs loaded penicillin by agar plate diffusion method. Inclusive, according to that results , the new nanocomposite, AgNPs -loaded penicillin, showed the highest antibacterial effects, against tested pathogenic bacteria, compared to penicillin alone.