1. Alkali titration method is inquired and employed in the determination of the pectin-es-terase activity. 2. The PE is extracted from tomato pulp by Na2HPO4 at pH 8. It is more influenced by pH than extractant. 3. The PE is precipitated by (NH4)2SO4 at 11_??_70% saturated. The precipitated enzyme is stable at dry state. 4. Pectin solutin is decomposed by PE and produces acid, but this reaction is inhibited at pH 3.8. 5. The PE has opt. pH 6_??_7.5, and decomposes over 80% methoxyl groups in pectin. 6. The opt. temp. is 60°, and loses the activity at 80° 7. CaCl2 and (NH4)2SO4 accelerate the PE activity. 8. The enzyme does not decrasc the viscosity of pectin or pectic acid solution, and does not produce the reducing sugar. 9. The characters of the PE from tomato differs from the PE in mould or bacteria.