Abstract: An experiment was undertaken to study the effects of acetic acid or/and molasses on the quality of fermented total mixed ration silage. Treatments: silage fermented without additive (control), with acetic acid (0.3% fresh matter basis), with molasses (3% fresh matter basis), or with acetic acid+molasses. There were 20 silos per treatment. All silos were opened 45 d after ensiling; five silos per treatment were analysed to determine fermentation characteristics, the remaining silos were exposed to air for 12 d to evaluate aerobic stability. After 45 dall silages were of good quality having high lactic acid concentration, low ammonia/total nitrogen, low butyric acid and very little propionic acid. During aerobic exposure, lactic acid, acetic acid and water soluble carbohydrate tended to decrease in all silages. The pH of the control and molasses treated silages increased significantly to 5.70 and 6.50 respectively and ammonia/total nitrogen and yeast counts were higher than the acetic acid and acetic acid+molasses treatments after 12 days of exposure. However, adding acetic acid reduced ammonia/total nitrogen compared with the control. Lactic acid content in the acetic acid and acetic acid+molasses silages increased during the early stages of aerobic exposure and then slowly decreased. Undesirable bacteria and yeast counts in the acetic acid treatment remained at low levels during aerobic exposure and the pH remained at about 4.50. It is concluded that adding 0.3% acetic acid maintained fermentation quality and improved the aerobic stability of fermented total mixed ration silage.