The magnetic properties and amorphous formation ability of Pr-based alloys have been reported and discussed. In this paper, Pr₉₀Fe₁₀ alloys were studied to reveal the solidification behavior associated with undercooling, magnetic properties of the metastable phase, and relation between undercooling and metastable phase formation by using the gas flow levitation method. The samples were solidified at various cooling rates from approximately 50 K/s to approximately 270 K/s. Undercooling increased with the cooling rate. According to the results of the SEM-EDS analysis, the Pr₉₀Fe₁₀ samples that solidified at high undercooling conditions in eutectic reactions consist of the primary α-Pr, eutectic α-Pr, and metastable phases whereas the samples that solidified at low undercooling conditions in eutectic reactions consist of the primary α-Pr, eutectic α-Pr, and Pr₂Fe₁₇ phases. Additionally, the magnetic properties changed due to the undercooling.