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Chemical composition, microbial rumen fermentation, energetic values and degradation of some Saudi Arabia sub-tropical browses were investigated in comparison with alfalfa hay as a high quality roughage using Hohenheim gas test in vitro. A gas test technique was performed using buffered rumen fluid collected from three rumen fistulated sheep. Cumulative gas production was recorded at 3, 6, 9, 12, 24, 48, 72 and 96 h of incubation in vitro. The investigated sub-tropical plants were blue panic (Panicum antidotale), moringa (Moringa peregrina), leucaena (Leucaena leucocephala). prosopis (Prosopis juliflora), casuarina (Casuarina glauca) and acacia (Acacia saligna). The sub-tropical plants were collected at the dry season in Saudi Arabia. Alfalfa and leucaena plants had the highest crude protein (CP) content, while the blue panic and moringa had the lowest value. The ether extract (EE) content of moringa and casuarina plants was 5.4 and 3.0%, respectively. The neutral detergent fiber (NDF) and acid detergent fiber (ADP) were higher in blue panic, acacia and moringa, while the prosopis and casuarina plants showed the lowest content of the fiber constituents. The secondary compounds analysis showed negligible contents of these feeds for total phenol (TP), total tannins (TT) and condensed tannins (CT) except moringa plant. The potential gas production was highest (p<0.05) for prosopis, alfalfa and blue panic plants, while the moringa plant recorded the lowest gas production. Leucaena, casuarina and moringa plants had the longest lag time (L, h(-1)) and lowest rate of gas production (mu h(-1)). The longest L value (2.339 and 1.95 h(-1)) was noted with leucaena and casuarina plants, while prosopis plant showed the short L value (0.617 h(-1)). There were wide variations among investigated plants in rumen fermentation characteristics, degradation and energetic values. The ranking order of the investigated plants on the basis of their true degradation of dry and organic matter was prosopis>leucaena>casuarina>blue panic>moringa>acacia. Concentration of NH3-N was high (p<0.05) in prosopis, blue panic and alfalfa hay, while in moringa plant appeared the low concentration (26.0 mg/100 g buffered rumen fluid) of NH3-N. The prosopis showed the highest (p<0.05) volatile fatty acids concentration. In conclusion, significant variations in in vitro fermentation and degradation were observed among different browse species collected from Saudia Arabia through the dry season. The results suggest that prosopis, leucaena and blue panic plants might be promising alternative feed resources and it could be incorporated in ruminants feed mixtures to replace conventional roughage sources (alfalfa) without major problems.