Forty eight 4-month-old Awassi male lambs (initial bodyweight 23.5 ± 1.3 kg) were used in a 70-day trial to evaluate the effects of supplemental AcidBuf (calcified seaweed extract) with different levels of salt (sodium chloride) on ruminal fermentation and tissue morphology of growing lambs. Animals were individually housed in shaded pens and randomly divided into 6 groups of 8 lambs each. The dietary treatments were: 1) no added supplemental AcidBuf or salt (control group; the basal diet), 2) 0.4% added AcidBuf (A+S0.0), 3) 0.4% added AcidBuf + 0.4% added salt (A+S0.4), 4) 0.4% added AcidBuf + 0.8% added salt (A+S0.8), 5) 0.4% added AcidBuf + 0.12% added salt (A+S1.2), and 6) 0.4% added AcidBuf + 1.6% added salt (A+S1.6). The basal diet was used a commercial total mixed ration, containing 1.95 Mcal M_Em and 13.0% CP/kg. Rumen fluid samples were collected from all lambs at 0, 2, 4 and 8 hours after feeding during day 1, 30, 60 and 70 to measure pH and fermentation profile. At the end of the study, lambs were slaughtered for evaluating the rumen papillae morphology. Lambs on the AcidBuf diets had less (P<0.05) pH, at after 0 and 2 h of the morning feeding and over the collection period, than those of lambs on the control diet. The length and the total surface of papillae were greater (P<0.05) in lambs fed only AcidBuf (A+S0.0) than those of lambs on the CON diet. Overall, these data indicate that AcidBuf and salt supplementation did not affect rumen fermentation and tissue morphology of growing lambs.