Izu-Oshima volcano commenced a series of eruptions on November 15, 1986 after twelve years’ quiescence. The renewed volcanic activity started as a summit eruption, later developed a drastic fissure eruption on November 21, and ended as a small summit eruption on December 18. Since 1975 we have repeated distance-measurement survey using an Electro-Optical Distance-Meter (EODM) in and around the summit caldera of the volcano. As a result we succeeded in the detection of a significant horizontal crustal deformation that occurred across the sequence of eruptions. The deformation of the summit caldera comprises a NE-SW extension and a NW-SE contraction. We infer from other related observational data that the greater part of the deformation resulted within the period of activity of the fissure eruption on November 21. The horizontal deformation of the summit caldera is explained, in outline, by the dike-intrusion model that TADA and HASHIMOTO (1987) proposed on the basis of the results of presice levelling survey. However, further study is necessary to get a strict conclusion.