The invention provides a square fluid sealing-in vibration isolation device with a novel structure; and the device can effectively reduce the stress concentration at the corner parts of four corners in a liquid chamber liable to become a cracking starting point in the past under the condition of not influencing and even improving self performances when higher loads on a compression side act on the square fluid sealing-in vibration isolation device, so that durability is improved. The square fluid sealing-in vibration isolation device uses a rubber elastomer for elastically connecting a first mounting component with a second mounting component; the rubber elastomer is provided with a pair of main elastic parts and a pair of side wall parts; the pair of main elastic parts are oppositely arranged in a first direction, and predominantly support loads input into the first mounting component; the pair of side wall parts are oppositely arranged in a second direction perpendicular to the first direction in a manner of crossing over the pair of main elastic parts; and gaps are formed between each main elastic part of the pair of main elastic parts and opposite surfaces of the pair of side wall parts in the second direction.