The objectives of this study were to estimate the digestibility of Juncus acutus and to investigate its effects on rumen cellulolytic bacteria to consider J. acutus as an alternative roughage source in ruminant nutrition. Juncus acutus samples were collected from three different stations in Kizilirmak Delta and their proximate analysis was carried out. Organic matter digestibility (OMD) and metabolisable energy (ME) values of J. acutus were estimated from gas measured by the in vitro gas production method. The effects of J. acutus on the abundance of rumen cellulolytic bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens and Ruminococcus albus were determined by real-time PCR method. Crude nutrient values of J. acutus collected from three stations were analysed. Mean OMD %, MEOMD and MEGP values of J. acutus from three stations were ranged from 42.64 to 42.48%, 6.78 to 6.82 MJ/kg DM and 5.05 to 5.26 MJ/kg DM respectively. Ruminal F. succinogenes, R. flavefaciens and R. albus abundance calculated from threshold (CT) values in rumen fluids obtained from 0 to 96 h incubations showed an increases in following order F. succinogenes > R. flavefaciens > R. albus. The CP % of J. acutus was found higher from cereal straw and close to low-quality alfalfa hay and dry meadow grass. Juncus acutus increased the amount of rumen cellulolytic bacteria. In the light of obtained results, it can be concluded that J. acutus may be considered as a new alternative roughage source in ruminant nutrition.