Abstract: Background and Objective: Leucaena (Leucaena leucocephala) is one of the potential legumes that is a source of protein feed for ruminants. Leucaena has approximately 24% protein. Leucaena usage is restricted because it contains the anti-nutrient mimosine (7.19%). Mimosine causes hair loss in sheep and inhibits the action of the hormone thyroxine. The purpose of this study was to evaluate the concentration of mimosine in the blood, rumen, urine, faeces, blood metabolites and thyroid hormones of sheep fed rations containing different levels of leucaena leaf meal. Methodology: There were two kinds of treatments: P1 = Napier grass 60+15% Gliricidia sepium+15% Leucaena leucocephala+10% Pollard and P2 = Napier grass 60+30% Leucaena leucocephala+10% Pollard. This experiment used a randomized block design. The variables observed in this study were the concentration of mimosine in the blood, rumen, urine, faeces, blood metabolites and thyroid hormones. Results: The results showed that different levels of leucaena leaf meal did not have significant effects on the mimosine concentration in the rumen, blood, urine, faeces, blood metabolites and thyroid hormones. Mimosine disappearance from consumption to excretion was between 34-68%. Conclusion: The addition of 30% Leucaena leucocephala leaf meal could be used without a negative effect on blood metabolites and thyroid hormones of sheep.