Increasing antimicrobial resistance in nontyphoid Salmonella species has been a serious problem for public health worldwide. The high rate of resistance is hampering the use of conventional antibiotics, and growing resistance to newer antimicrobial agents is aggravating the situation. The circumstances of occurrence and spread of antimicrobial resistance are complex; however, a major cause is the widespread use of antimicrobial agents in food animals, particularly in animal feed. Genetic analysis has indicated that the source of resistance is frequently a transferable plasmid. Recent studies have revealed that some serotype-specific virulence plasmids form hybrid plasmids through recombination with resistance plasmids or acquire gene cassettes consisting of multiple resistance genes. Such evolutionary events provide a virulent strain the advantage of survival in an unfavorable drug environment. In view of the serious implications associated with drug-resistant Salmonella species, a more deliberate use of antibiotics in both human medicine and animal industry is warranted. Continued surveillance of antimicrobial resistance and use of antimicrobial agents in food animals is also indispensable.