There has been an increasing interest in the use of natural plant materials as alternative food preservatives. We examined the antimicrobial effects of natural plant materials used as additives against foodborne pathogens in laboratory media and Sulgidduk, oriental-style rice cakes. Cinnamon, mugwort, and garlic powder solutions (3%) were tested for their antimicrobial activities against pathogens in laboratory media. Sulgidduk prepared with different amounts of cinnamon powder (1, 3, and 6%) was inoculated with a Staphylococcus aureus or Bacillus cereus cocktail. The samples were air or vacuum packaged and stored at 22 ± 1°C for 72 h, and microbial growth was determined. Cinnamon powder showed more inhibitory properties against pathogens such as Salmonella enterica serovar Typhimurium, Escherichia coli O157:H7, Listeria monocytogenes, S. aureus, and B. cereus than did mugwort or garlic powder. The populations of S. aureus and B. cereus in Sulgidduk containing cinnamon powder were significantly lower than in the control during storage time. Different packaging methods did not result in a significant difference in pathogen growth. In a sensory evaluation, Sulgidduk containing 1 and 3% cinnamon powder did not significantly differ from the control sample in any of the attributes tested other than flavor. These results indicate that natural plant materials such as cinnamon powder could be used as food additives to improve the microbiological stability of rice cakes.