The concept of utilizing a Zr-Er alloy in high-burnup fuel claddings in light water reactors has been proposed. Er in a Zr alloy is expected to act as a burnable poison that reduces the excess reactivity. However, the required physical properties for practical realization of Zr-Er alloys have yet to be fully understood. Here, we prepared Zr-Er alloys with various Er contents and characterized the phase state, Young’s modulus, and thermal conductivity. The effect of Er content on the thermal and mechanical properties of the alloys was investigated.