This paper presents new results of a study of tuffs from Upper Miocene sedimentary succession in Eastern Georgia and describes their secondary alterations. These data are important for regional correlations, the dating of rocks, and the identification of magmatic sources of pyroclastics. Samples from Upper Sarmatian (Eldarian suite) and Maeotian-Pontian (Shirakian suite) were collected at the Udabno section in Kakheti. The samples were examined using an optical and scanning electron microscope and an X-ray diffractometer. The chemical composition of the studied pyroclastics (fragments of volcanic glass) is defined as acid volcanic. Upper Sarmatian tuffs most likely correspond to the initial pyroclastics of rhyolitic composition with a predominance of sodium over calcium. The Maeotian-Pontian tuff most likely refers to the initial pyroclastics of dacitic composition with a predominance of calcium over sodium. The studied rocks have a different degree of secondary alteration, characterized by the predominant development of smectites and zeolites (analcime and heulandite/clinoptilolite). Secondary alterations of studied tuffs reflect the characteristics of the original pyroclastics. The Na-zeolites (analcime) are typical of Na-rich pyroclastics, while the Ca-Na zeolites (heulandite/clinoptilolite) are characteristic of volcanic rock with a high content of Ca. Secondary alternation was accompanied by the removal of K + from volcanic material. Smectite was formed at the initial stages of secondary alterations preceding further intensive zeolitization. The development of idiomorphic zeolite crystals after smectite formation in the pores was revealed. In contrast to the Miocene tuffs of the Kerch-Taman region, the radiometric age dating of the studied Upper Sarmatian and Maeotian-Pontian tuffs of the Udabno section is hardly possible because of their secondary alterations.