Pine cones of Pinus parviflora Sieb., et Zucc, were extracted successively with 5% NaHCO3, 3% NH4OH, 1% NaOH and 4% NaOH, and the extracts were tested for ability to induce antimicrobial activity in mice infected with Staphylococcal aureus. Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Candida albicans, or Salmonella enteritidis. These alkaline extracts were potent against the first 5 of these strains of microorganisms, and the activity was recovered mostly from their acid-precipitates at pH 5. After further fractionation on a Sephadex LH-60 column, the highest molecular weight fraction was most potent. Chemical structures in these bioactive fractions were assumed to be lignin-related structures, based on spectral data from UV, NMR and IR spectroscopy.