Twenty four Friesian bulls with a mean live body weight of 450±32 Kg, belonging to Sakha experimentral farms were used in the present study under the same dietary regime. The rumen volume and flow rate were estimated from the rate of decline in concenteration of a marker in the rumen fluid following a single ruminal injection. The results of several determination methods of rumen volume  using different markers ( lithium sulphate, polyethelienglycol, Cr-EDTA and Cr₂O₃ ) gave similar values with differences ranging from 6 to 18%. Rumen volumes as determined by different methods are significantly (p < 0.01) correlated with live body wieght. The correlation coefficient values ranged from 0.60 to 0.79. The direct determination of rumen volum were done by substituting rumen content by water ( physical volume) gave rumen volume values ranged from 30 to 36% higher than that estimated by using marker methodes. The flow rate of rumen contentes was affected significantly (p < 0.05) according markers.The values of flow rate ranged from 3.5% to 4.9% from the total volume per houre. This values equipoise disharge rate ranged from .84 to 1.25 times per day. Using  Polyethyleneglycole gave the nearst estemated value to the true rumen volume (Physical volume) r =0.92 comparing with the rest used markers.