The aim of the study was to compare different parts (leaves, fruits, seeds) of three Rosaceae species (Rosa canina, Crataegus orientalis and Crataegus monogyna) in terms of nutrient composition and in vitro ruminal fermentation parameters. The in vitro total gas production levels of the leaves of all Rosaceae species were similar (P > 0.05). The in vitro total gas production of R. canina fruits and seeds was lower compared with those of C. orientalis and C. monogyna fruits (P = 0.001) and seeds (P = 0.008). The in vitro methane production of R. canina seeds was lower (13.66%) than that of the Crataegus seeds (16.50%–16.80%; P < 0.01). The methane production of the leaves and fruits of all three Rosaceae species was similar (P > 0.05). There were no differences among the in vitro short-chain fatty acid (SCFA), organic matter digestibility (OMD), metabolizable energy (ME) and net energy lactation (NEL) levels of leaves of the three Rosaceae species. The ME, NEL, SCFA and OMD levels of Rosaceae fruits and seeds differed significantly (P < 0.01). The Rosaceae fruits and seeds could be ordered as C. orientalis > C. monogyna > R. canina in terms of ME, NEL, SCFA and OMD. The leaves of the Crataegus species, when compared in terms of roughage source for grazing animals in scrublands, contain a moderate level of crude protein and fibre, but the crude protein level in the leaves of R. canina was rather low. The leaves and fruits of all tested Rosaceae species and the seeds of R. canina can be used as rumen modulators with an anti-methanogenic effect. These results suggest that Crataegus leaves have the advantage of maintaining their nutritive value for ruminants throughout the dry season (especially in late summer) when grasses dry up.