Recent achievements in seismic studies of volcanic structure are summarized in this article. Seismic studies of volcanic structure was enhanced and advanced extensively in 1990's. The advance of the study was supported by new compact and light weighted digital recorders and by popularization of 3-D travel time inversion algorithm. Seismological characters in volcanic structure were revealed and were represented as high and low velocity anomalies, concentrated seismicity and intra-crust seismic reflectors. Important problems for seismic studies of volcanic structure are presented as more penetration, more resolution and more quantification of seismic characters in active volcanoes, which should be solved in next decade.