The aim of current experiment was to determine the effects of honey locust pods (HLP) as carbohydrate source on the fermentation, aerobic stability, in vitro gas production, microbiological characteristics of alfalfa (Medicago sativa L.) silages in laboratory conditions. Honey locust pods was applied at 0 (control), 20, 40, 60, 80 and 100 g/kg DM levels to alfalfa forage harvested at full bloom stage and chopped to about 1.5-2.0 cm length. Supplementation of HLP had a significant (P<0.01) effect on the chemical composition of alfalfa silage depending on the level of HLP supplementation. The supplementation of HLP significantly (P<0.01) decreased the crude protein (CP), ether extract (EE), crude ash (CA), neutral detergent fiber (NDF) and acid detergent fiber (ADF) whereas the water soluble content (WSC) and total tannin (TT) increased with increasing level of HLP. The supplementation of HLP decreased the pH, acetic acid, butyric acid and ammonia-N (NH3-N) whereas the supplementation of HLP increased the lactic acid and propionic acid content of alfalfa silage (P<0.01). The supplementation of HLP significantly (P<0.01) increased the in vitro gas production, digestible organic matter (DOM), metabolizable energy (ME), lactic acid bacteria and yeast whereas mould decreased. On the other hand the supplementation of HLP improved the aerobic stability of alfalfa silage decreasing the CO2 production. As a conclusion the HLP can be used as a silage additive in the level of 80 and 100 g/kg DM when alfalfa plant is ensiled.