The aim of the study was to evaluate the effects of calcium carbonate (CCA) on the fermentation quality, aerobic stability and microbial counts during the aerobic deterioration of two high moisture total mixed ration (TMR) silages. The alfalfa hay, sweet potato residue, maize flour, soybean meal, molasses and vitamin-mineral supplement were mixed on a dry matter (DM) basis in the rations of 40:30:18:9:2:1, respectively, to prepare TMR. The moisture level of TMR silage was adjusted to 600 (medium) and 750 g/kg (high) before ensiling with 0, 5, 15 and 25 g/kg CCA (on a fresh weight (FW) basis). The fermentation quality, chemical composition, microbial counts and aerobic stability of TMR were assessed after 150 days of ensiling. It was observed that pH, lactic acid, acetic acid, ammonia nitrogen and the population of lactic acid bacteria (LAB) were influenced (P < 0.05) by moisture level, CCA application and their interaction. Likewise, adding increasing amounts of CCA increased aerobic stability (P < 0.05) of the TMR silage from 18.4 to 23.7 days and from 3.7 to 11.5 days at medium and high moisture level, respectively. Moreover, it was observed that the growth of yeasts and aerobic bacteria were inhibited by the CCA application during the aerobic deterioration. The application of CCA additive is an appropriate strategy for improving fermentation quality and aerobic stability of both relatively high moisture TMR silages.