A manufacturing method of a magnetic random access memory (MRAM) cell includes the following steps. A magnetic tunnel junction (MTJ) film stack is formed on an insulation layer. An aluminum mask layer is formed on the MTJ film stack. A hard mask layer is formed on the aluminum mask layer. An ion beam etching (IBE) process is performed with the aluminum mask layer and the hard mask layer as a mask. The MTJ film stack is patterned to be a patterned MTJ film stack by the IBE process, and at least apart of the aluminum mask layer is bombarded by the IBE process for forming an aluminum film on a sidewall of the patterned MTJ film stack. An oxidation treatment is performed, and the aluminum film is oxidized to be an aluminum oxide protection layer on the sidewall of the patterned MTJ film stack by the oxidation treatment.