Three speciesof plants: Nerium oleander L., Thevetia peruviana (Pers.) K. Schum, and Cerberaodollam Gaertn., in the family Apocynaceae containing cardiac glycoside were studied microscopically using free-handed thin section and peeling methods for fresh samples. Leaves and flowers of each plant were artificially digested with chemicals and controlled temperature.After the digestion, the samples were collected at a specific time point (30 min, 1-5, 24 and 48 hrs) and comparing anatomically with the undigested fresh samples. The results showed that distinguishable and specific microscopic structures were found in each species. The important microscopic features in leaves are the types of stomatal complex, trichomes, calcium oxalate crystals, the number of hypodermal layer and palisade mesophyll. For the flowers, the specific characteristics are the types of trichomes, shape and the aperture of pollen grains. Comparison between the undigested and digested samples using the significant anatomical structures had been done. The results show that the digested plant material can be identified microscopically. Moreover, the significant anatomical structures in the digested samples show unchanged features throughout the time of digestion. The anatomical structures had been established as the identification parameters which can be employed for plant materials found in gastric contents of forensic cases.