This study was practical for evaluating the difference in characterization and effects on pathogenic bacteria between AgNPs synthesis by biological method by using marine green alga Ulva fasciata and chemical method by sodium borohydride (NaBH4). Also examines the synergistic or antagonisms that applied by loading AgNPs synthesis by biological and chemical methods on antibiotics. The results point to that there is difference in characterization of AgNPs synthesis by various methods that determined by UV-vis absorbance, Transmission electron microscope (TEM), Zeta potential and X-ray Diffraction techniques (XRD). Antibacterial action of AgNPs experienced against eclectic pathogenic bacteria such as Gram negative bacteria (E. coli O157 (KY797670), Aeromonas hydrophila and Salmonella enteric subsp. salamae (Em.1-EGY015) and Gram positive bacteria (Bacillus cereus and Staphylococcus aureus); meanwhile, Biological synthesis AgNPs had more effective against pathogenic bacteria than chemical synthesis AgNPs. The minimum inhibitory concentration (MIC) of AgNPs creation by biological method is less than that created by chemicals methods. The synergetic or antagonism of AgNPs loading in antibiotics (Norfloxacin, Cefepime, Levofloxacin, Amoxicillin/Clavulanic Acid, Ampicillin/Sulbactam, Cephalexin, Ofloxacin, Neomycin, Cefoperazone and Amikacin) had different effects according to antibiotics, pathogenic bacteria and methods of synthesis AgNPs.