The objective of the test was to prepare the microcapsule of beta-cyclodextrin / oregano essential oil and study its antimicrobial activity. First, Beta-cyclodextrin was selected as the embedding material to get the oregano oil microcapsule. Second, SEM was used to observe the external appearance of the inclusion complex. Next, the two methods of TLC and IR were used to check whether the complex was successfully prepared or not. Then the embedding rate was determined with the help of UV spectrophotometer and some certain processions. Last, significant antimicrobial activities of the microcapsule were tested against Escherichia coli and Aspergillus oryzae. The microcapsule of beta-cyclodextrin / oregano essential oil was successfully prepared with an embedding rate of 73%, and it had a good antimicrobial effect. The experiment has achieved its expecting purpose, i.e., preparing the liquid of oregano essential oil into be solid power and meanwhile keeping the oil′ s antimicrobial activity.