The g-factor of the extremely proton-rich nucleus 23Al (T 1/2 = 0.47 s) has been measured by means of the β-NMR method for the first time. The g-factor were determined as |g| = 1.557(88) from the obtained NMR spectra. From the comparison between the experimental value and the shell model calculation, the spin parity of the ground state of 23Al was determined as Iπ = 5/2+. Thus, the magnetic moment of 23Al was determined as |μ| = 3.89(22)μN. © 2005 IOP Publishing Ltd.