A rubber vibration insulator for use in a vibration insulation device integrated into precision instruments such as acoustic, computer-associated and game instruments, which insulator has a low hardness, a small compression set, a large loss tangent and a small temperature dependence and can be prepared by curing a rubber composition comprising 100 parts by weight of a partially crosslinked butyl rubber and 50 to 200 parts by weight of an extender component as well as a vulcanizing agent.