High-voltage pulse discharges were generated between underwater two metallic Tin (Sn) wires in order to synthesize nanoparticles. Nanoparticles were synthesized in pure water or aqueous gelatin solution. In pure water, Sn and SnO 2 particles of approximately 5 nm in diameter were synthesized. However, synthetic particles in pure water had a problem of aggregation. The influence of gelatin solution on the particle size and dispersibility of the synthetic particles was investigated. In 10 mg/L gelatin aqueous solution, metallic Sn particles of approximately 40 to 400 nm in diameter were synthesized and were dispersing separately. From the peak width of X-ray diffraction (XRD) spectrum, the particle size was estimated using the Scherrer's equation. As a result, the minimum size was approximately 20 nm at 2 mg/L of aqueous gelatin solution. 金属スズからのナノ粒子合成を目的と して，２本の金属スズ線を，先端を対向させて水中に浸漬し，両スズ線間で高電圧パルス放電を発生させた。液体として，純水とゼラチン水溶液を用いた。純水中では，直径約 5 nm の Sn と SnO2 からなるナノ粒子が合成 されたが， 粒子の凝集がみられた。 10 mg/L のゼラチン水溶液を用いた場合， 直径約 40 ～ 400 nm の金属スズナノ粒子が合成され， 粒子の凝集はみられず分散していた。合成粒子の X 線回折 (XRD)スペク トルにおけるピークの半値幅から，シェラーの式を用いて 粒子径を算出した。その結果，粒子径が最小となるのはゼラチン水溶液が 2 mg/L のときで，そのときの直径は約 20 nmとなった。