To determine the effects of acid precipitation on Japanese black pine (Pinus thunbergii Parl.) with and without mycorrhizae (Pisolithus tinctorius (Pers.) Coker et Couch), 1-year-old seedlings were exposed to simulated acid mist, pH 3.0, for 10 min per day twice a week for 3 or 4 months. Simulated acid mist adversely affected the transpiration rate and lowered the extractable phosphorus content of seedlings, but seedlings with mycorrhizae were less affected by acid mist than were nonmycorrhizal seedlings. Simulated acid mist also retarded mycorrhiza formation. Key words: mycorrhizae, phosphorus content, Pinus thunbergii, Pisolithus tinctorius, simulated acid mist, transpiration rate.