The alteration products of Tertiary pyroclastics exposured within an area which cover Uzunkopru, Meric, Kesan, Gelibolu, Enez and Tekirdag in Thrace, Turkey have been investigated. The neoformation minerals in dacitic, andesitic pyroclastics are smectite, illite, kaolinite, heulandite-clinoptilolite, quartz, opal-CT and calcite. Clay and zeolite group minerals are the major components of the rocks in some localities, so that they have economic importance. The pyroclastics in the zone of Gelibolu-Kesan-Uzunkopru had been undergone into zeolitization (heulandite type) widely and also clay alteration. In other localities, however, clay type mineralization is predominant showing fresh glass + clay minerals association. Whole rock compositions have revealed the alteration steps between the fresh (or partly altered) and mostly altered rocks.