AlFe2B2 was synthesized by arc-melting to investigate its magnetic properties. The magnetic properties of AlFe2B2 with impurities are different from those of pure AlFe2B2. In this study, an as-cast sample and an annealed sample followed by acid treatment were prepared to understand the magnetic properties of pure AlFe2B2. In the powder X-ray diffraction measurements, a pure AlFe2B2 phase was confirmed after annealing followed by acid treatment. Various magnetic properties were investigated by using superconducting quantum interference device (SQUID) measurements for the as-cast and the post-treated samples. Saturation magnetization and effective magnetic moments of the post-treated sample are close to the theoretical values of pure AlFe2B2. The maximum magnetic entropy change (-Delta S) of pure AlFe2B2 is 6.95 J/kg.K at 5 T. Pure AlFe2B2 shows a positive slope in the Arrott plots corresponding to a second-order magnetic transition. Magnetic transition temperatures estimated from dM/dT, the Arrott plots, and the Curie-Weiss law are mutually complementary.