A study was conducted to investigate the effects of different total mixed ration diets (TMRs) with three different levels of NDF on growth performance, metabolic profile and rumen characteristics in Naemi lambs. Fifty growing Naemi lambs at age of three months with an average bodyweight of 27.77 ±1.09 kg were randomly distributed to five different treatments, ten lambs each, as follow: 1. Alfalfa hay and barley grain (ABG); 2. Pelleted alfalfa hay and barley (PAB); 3. TMR1 (25.67% NDF); 4. TMR2 (30.88% NDF); and 5. TMR3 (55.93% NDF). Lambs were housed in an individual pen for 90 days. Lambs were weighed every two weeks and feed intake was recorded weekly. Rumen fluid samples were collected monthly after 2, 4 and 8 hours of feeding for pH, VFAs and NH3-N determination. Blood samples were collected monthly for different metabolic analysis. At the end of the trial, six lambs from each group were randomly selected and slaughtered for rumen coloring. The results of this trial showed a significantly higher total body weight gain in lambs fed TMR1 and TMR 2. A significantly higher FCR in lambs fed TMR3 compared with all other treatments. The rumen color of lambs fed TMR2 was significantly (P < 0.01) lighter compared with all other groups except lambs fed ABG. Pelleting the alfalfa hay and barley affect the rumen color to be darker compared to ABG. Regarding the rumen fluid pH, lambs in ABG and TMR2 groups were significantly higher after eight hours of feeding compared with all other dietary groups. In conclusion, feeding growing lambs with TMRs containing 30% NDF, leads to obtain a safer and suitable rumen characteristics, microbial fermentation and growth performance.