Six complete rations based on bean straw and containing different dietary nitrogen sources were used to study their influences on rumen liquor characteristics. Soybean meal (SBM), corn gluten meal (CGM) and cottonseed meal (CSM) were used as the sole source of protein in the tested rations or in combination with 1%urea (U). Diets were formulated to be isonitrogenous and isocaloric (14%CP and 64% TDN). Thirty-six  Finn-Ossimi crossbred male lambs (22kg average body weight and 4 months age) were used in a fattening trial for 106 days. The animals were divided into 6 similar groups. Each one was assigned to receive one of the following experimental rations: SBM, CGM, CSM, SBM+1%U, CGM+1%U and CSM+1%U. Rumen liquior was obtained from male lambs using a stomach tube at 0, 3 and 6 hours postfeeding. Results obtained could be summarized in the following: 1- Dietary N source did not affect significantly the pH value, except SBM group which had higher (P<0.05) pH value compared with the other groups. 2- Values of rumen pH increased 3hrs post feeding and then decreased 6hrs post feeding, where it lies between 6.22-6.51 on the average . 3- Urea supplementation decreased ruminal pH value, except CSM group. 4- Ruminal NH₃-N and VFA^,s concentration had, in general the normal distribution curve, since they increased 3hrs after feeding then decreased 3hrs later. 5- Dietary N sources affected (P<0.05) NH₃-N concentration in ruminal fluid, where natural proteins, in general had higher values compared with urea supplemented diets. 6- SBM had the highest (P<0.05) NH₃-N value (14.15mg/100ml), while CGM+1%U had the lowest (P<0.05) value (10.73 mg/100ml). 7- Incorporation of U in the diets reduced (P<0.05) NH₃-N in rumen liquor. 8- Ruminal VFA^,s concentration for the experimental rations lies between 8.34 and 10.54m equv/100ml, with SBM+1%U had (P<0.05) the highest value (10.54m equiv/ 100ml) and CSM had (P<0.05) the lowest value (8.34 m equiv /100ml). 9- Dietary N sources affected (P<0.05) ruminal VFA^,s concentration. Moreover, U, supplementation increased (P<0.05) VFA^,s concentration in rumen liquor. 10- Dietary N sources affected (P<0.05) the molar proportion of VFA^,s. 11- Supplementing diets with urea increased (P<0.05) the molar proportion of butyric acid, however it reduced (P<0.05) the molar proportion of both acetate and the ratio of acetat/propionate.