The present study aims to enhance the efficiency of anaerobic sludge microorganisms to produce hydrogen (H.sub.2) through various pre-treatment methods. The various pre-treatment methods such as base, acid, chloroform, heat shock, freezing and thawing have enabled to isolate acidogenic bacteria with higher bio H.sub.2 producing activity in an anoxic environment. From these various treatments, bacteria were isolated and screened for bio H.sub.2 capabilities. Among the one bacterial strain, AH4 strain showed maximum cumulative H.sub.2 production and Hydrogen Yield (HY) using 100% diary anaerobic sludge. AH4 strain was identified as Acinetobacter junii using 16S rRNA gene sequence and used for further experimental analysis. Biohydrogen productions of Acinetobacter junii were measured at different experimental setup such as various pH levels (5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0) and different substrate concentration (10-100%) of dairy anaerobic sludge substrate. At pH 7.5 and 60% substrate concentration, the strain AH4 Acinetobacter junii displayed the maximum cumulative H.sub.2 production of 945.7 ml/L and H.sub.2 yield 1.35 mol H.sub.2/ mol glucose. Based on our results, we concluded that Acinetobacter junii can be used as a promising bio agent for hydrogen production on a large scale using dairy anaerobic sludge as substrate.Key words: Bio hydrogen, Dairy industry anaerobic sludge, Pretreatment, Optimization, Batch experiment.