The antimicrobial activities of Smilax china L. against spoilage bacteria isolated from Mang-gae rice cake were investigated and the storage stability of the Mang-gae rice cake was enhanced. Spoilage bacteria, which cause Mang-gae rice cake to rot, were isolated from commercial Mang-gae rice cake, and most of the isolated strains were identified as Bacillus sp. After the leaves, roots, shoots, and stalks of the Smilax china L. were extracted using 50% ethanol as the solvent, their antimicrobial activities were investigated using the paper disc method by treating them with 50 μL of Bacillus cereus, which is known as a major pathogenic micro-organism in foods that contain starch, as the test organism. The antimicrobial activities of the extracts were compared according to the size of the clear zones around the paper discs. The root extract showed significant antimicrobial activities. When red beans, which are used as stuffing for Mang-gae rice cake, were treated with the root extract of the Smilax china L., the viable cell count of the Mang-gae rice cake was 5.04 Log CFU/g after 48-hr storage, and the cake showed significantly slower growth of bacteria than with commercial products. These results show that treatment of red beans with Smilax china root extract could improve the storage stability of Mang-gae rice cake.