A vibration isolator capable of efficiently increasing damping against inputted vibration provided by a fluid flowing in a restrict passage and also suppressing the rise of a dynamic spring constant when vibration is inputted therein.In the vibration isolator 10, a pair of pressure receiving fluid chambers 46 and 48 are disposed, between an outer cylinder 12 and a mounting member 20, at one end side and at the other end side along a main amplitude direction. Since a rubber elastic body 22 changes the internal volumes of the pair of pressure receiving fluid chambers 46 and 48 in directions opposite to each other, and fluid flows from the pressure receiving fluid chambers 46 and 48 to an auxiliary fluid chamber 30 through one of orifices 62 and 64 and flows from the auxiliary fluid chamber 30 to the pressure receiving fluid chambers 46 and 48 through the other of the orifices 62 and 64. As a result, since a fluid pressure in the auxiliary fluid chamber 30 is kept approximately constant, the fluid in the pair of pressure receiving fluid chambers 46 and 48 smoothly flows, with a low resistance, into the auxiliary fluid chamber 30 through the orifices 62 and 64. Therefore, any rise of the fluid pressure in the pressure receiving fluid chambers 46 and 48 may be suppressed and, accordingly, the rise of the dynamic spring constant may be suppressed.