The influences of Y content and initial mold temperatures on the hot tearing susceptibility (HTS) of binary Mg-Y alloys were investigated using a constrained rod casting (CRC) apparatus, which is equipped with a load cell and data acquisition systems. The hot crack formation was monitored during CRC experiments. The experimental results show that HTS first increases with increase in the Y content, reaches the maximum at about 1.5 wt% Y and then decreases with further increase in the content of Y. The severest of hot tearing is found in Mg-1.5 wt% Y alloy which is due to its large columnar grain structure, wide solidification range, and small amount of eutectic. The resistance to hot tearing is apparently improved by increasing the initial mold temperature. ProCAST simulation software was used to predict the hot tearing of Mg-Y alloys in CRC. The simulation results show a good agreement with the experimental measurements. The numerical simulations will be helpful and valuable to optimize the alloy composition and casting parameters to minimize the hot tearing defects.