We report here the influence of block number and polyester weight fraction on the properties of a series of poly(ether ester) multiblock copolymers (mBCPs), poly(butylene terephthalate)-block- poly( tetramethylene oxide) (PBT-b-PTMO-bPBT)(n), with the same PTMO segment length. These mBCPs are double-crystalline polymers, where the melting temperature and crystallinity of PBT increase with the polyester weight fraction. The PBT and PTMO blocks undergo phase separation at room temperature to form a plausible bicontinuous disordered structure. With the increment of the block number, the phase-separation-domain size decreased. As a result, the crystallinity of PBT and PTMO decreases, while the strength and elongation at break of mBCPs increase significantly due to the enhancement of bridging segments between different domains. The increment of the polyester weight fraction significantly enhances mBCPs' strength and Young's modulus but decreases their elongation at break. Our results enrich the understanding on the phase behavior of mBCPs, and the structure-property relationship revealed here would be useful for the design of poly(ether ester) elastomers with desired properties.