Background: This study was a qualitative analysis of street heroin in Bihar. The aim of the study is to examine the purity and composition of street grades samples of heroin sized from arrests of street level users and dealers in Bihar. Analysis of composition of illict drug can support in comparative analysis in linking two or more sample together. It can also provide information about their distribution route. Materials and Methods: Eleven suspected samples of heroin were selected seized from street- level users/ dealers in Bihar and referred to Forensic Science Laboratory, Bihar, Patna. Physical characteristics of the samples were analyzed for their colour and appearance. Marquis Test and Frohde Test were performed for presence of diacetyl morphine. Gas-Chromatography/Mass Spectrometry screening was conducted to identify the adulterants and conformation of heroin. The chemical formulation (Chloride or Base) was confirmed using precipitation tests with Silver Nitrate and Barium Chloride solutions. Molish’s Test and Benedict’s Test were done for identification of sugar diluents. Result: Eight out of eleven samples looked like fine powder, the rest were more granular. Preliminary colour tests were performed for diacetyl morphine. Positive result indicates all of the eleven samples contained diacetyl morphine. Purity was assessed by means of Gas-Chromatography/Mass Spectrometry. Different manufacturing impurities and adulterants were also found. Anion test for chemical formulation was performed indicates Basic and Hydrochloride nature of heroin. Carbohydrate test also shown positive. Conclusion: These profiles latter can be used in comparison of illegal heroin specimens in different areas and also allow us to determine the geographical place where heroin was made.