In the course of screening for new bioactive substances, a novel nucleoside named oxetanocin was isolated as crystals from the fermentation broth of Bacillus megaterium NK84-0218. The structure was determined to be 9-[(2R,3R,4S)-3,4-bis(hydroxymethyl)-2-oxetanyl]adenine by X-ray crystallographic analysis. This communication reports the production process, isolation methods (including Dowex 50WX8, carbon, Diaion HP-20, and silica gel chromatography), chemical properties (molecular formula C₁₀H₁₃O₃N₅, UV maxima at 259 nm (water), 257 nm (0.1N HCl), and 259 nm (0.1N NaOH), IR spectrum, and ¹H/¹³C NMR data), and biological properties (activity against herpes simplex virus-II with 50% inhibition at 5.8 μg/well, cytotoxicity against Vero cells with 50% inhibition at 132.6 μg/well, inhibition of HeLa cell growth with an IC₅₀ of 47 μg/ml, strong antibacterial activity against Staphylococcus aureus 209P, Bacillus subtilis PCI 219, Bacillus polymyxa IAM 1210, and B. cereus IAM 1072 (MIC < 0.1 μg/ml), and no acute toxicity in mice at a dose of 200 mg/kg) of oxetanocin.