Streptozotocin, an antibiotic produced by Streptomyces achromogenes, is a broad spectrum antibacterial agent and also has antitumor activity in both in vitro and in vivo systems. This study presents evidence supporting the assignment of structure I to streptozotocin. Streptozotocin has the molecular formula C₈H₁₃N₃O₇, decomposes with gas evolution at ~115°C, and has no titratable groups. NMR shows an N-CH₃ group (δ 3.15, 3H) and no C-CH₃. Acetylation yields tetraacetate II. Alkali treatment produces diazomethane (suggesting N-nitrosomethylamide) and III, which hydrolyzes to CO₂ and D-glucosamine (indicating a urea derivative with glucosamine nitrogen). UV (λmax 228 nm, ε 6360) and IR (1700 cm⁻¹ carbonyl, 1530 cm⁻¹ N-N=O) support this. Structure I is established. Streptozotocin mutarotates to [α]²⁵D 39° in water. Synthesis via tetra-O-acetylglucosamine hydrochloride confirms the structure.