Ferritin, as an iron storage protein, has been considered to be a well-utilized iron supplement. However, the typical thermal processing of food rich in ferritin may affect the structure and function of ferritin as an iron supplement. Here, a plant ferritin (soybean seed ferritin, SSF) and an animal ferritin (donkey spleen ferritin, DSF) were used to analyze the changes in fundamental structure and iron content after thermal treatments (68 °C for 30 min, 100 °C for 10 min). Then, SSF and DSF after thermal treatment were administered intragastrically to mice to further evaluate its digestive stability and absorptivity after thermal processing. Results showed the secondary structure, oligomeric states, iron content, and digestive stability of DSF were maintained better than that of SSF after thermal treatments, indicating that DSF has a higher thermostability than SSF. Both SSF and DSF after thermal treatment exhibited higher absorptivity than untreated ferritins. SSF showed higher absorptivity than DSF whether heated or not.