Recent progress on petrological and geochemical studies on eruption products is reviewed especially related to three major eruptions in the last decade, 1990-95 Unzen, 2000 Usu and 2000 Miyakejima. Detections of essential magmatic fragments in the early eruptive products were critical for the evaluation of the progress of ongoing eruptions. Mineralogical studies were useful not only to identify essential materials, but also to estimate the depth and temperature of magma chamber and magma ascending processes. Systematic studies on volatiles both in melt inclusions trapped in phenocrysts and in volcanic gas have enabled to construct the quantitative models of the dynamic processes of magma. Petrological and geochemical estimations of the depth of magmatic processes are now becoming to be combined with the geophysical observations, and will be used together to construct more dynamic magma models in the near future. Experimental petrology to determine precise phycico-chemical conditions of magma and kinetics of crystallization and vesiculation will be the key studies in the future to assemble more quantitative information on magmatic activities and appropriately predict the change of ongoing volcanic activities. E-mail: k.uto@aist.go.jp