The nutritive values of leaves of Citrus grandis, Citrus aurantium, Citrus oranges, Citrus limon, and Citrus deliciosa were evaluated by chemical composition and in vitro gas production techniques. There were significant (p < 0.001) differences among citrus species in terms of chemical composition. Crude protein (CP) contents ranged from 123.0 to 148.3 g/kg DM. Neutral detergent fibre (NDF) and acid detergent fibre (ADF) contents were varied with species in the range 219.4-355.4 and 215.0-278.8 g/kg DM respectively. Condensed tannin (CT) contents were ranged from 5.9 to 10.2 g/kg DM. The PEG addition significantly (p < 0.001) increased the gas production and some estimated parameters of citrus tree leaves. However, species showed variable responses to polyethylene glycol (PEG) treatment. There were also significant (p < 0.001) differences among species in terms of gas production and estimated parameters. The OMD and ME contents of citrus leaves without PEG supplementation were ranged from 66.5 to 73.3% and 9.8 to 10.9 MJ/kg DM respectively. The improvement in gas production, organic matter digestibility (OMD) and metabolizable energy (ME) with PEG emphasized the negative effect of tannins on digestibility. The increase (%) in the estimated OMD and ME contents ranged from 5.5 to 9.8% and 5.7 to 10.2% respectively. All citrus tree leaves studied in this experiment have potential nutritive values indicated by high crude protein content, OMD, ME and low fiber values.