Four (4) samples of Spent Sorghum mash (SSM) with substrate to inoculums concentration of 10:1(w/w) were supplemented with 0.29, 0.33, 0.37, and 0.41% levels of methionine on dry matter(DM) basis. The same quantity of samples were compacted in four (4) jam bottles of equal volume to achieve anaerobic condition as much as possible and allowed to ferment for 4 days. The re-fermented spent sorghum mash (RSSM) samples were sun-dried for 3 days and subjected to analyses for proximate nutrient and amino acid compositions respectively.The DM% composition of SSM sample was significantly (P<0.05) higher than samples on 0.29, 0.33 and 0.39% methionine treatments. The crude Protein content of all samples on 0.29, 0.33, 0.39 and 0.41% methionine treatment did not differ significantly (P>0.05) but were significantly (P<0.05) higher than the control. The CP% was observed to increase linearly with increase in the levels of methionine supplementation. The CF% composition of sample on control were similar to that on 0.29% methionine treatment but significantly (P<0.05) higher than that on 0.33, 0.37, and 0.41% methionine treatments. The RSSM sample showed the availability of all essential amino acids except tryptophan (alanine, arginine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine and valine). The results of this study indicates increase in quantity of protein and the availability of essential amino acids after second stage fermentation of spent sorghum mash with methionine supplementation and can therefore be used in rations for non-ruminant animals in place of expensive conventional plant protein sources.