The portable laser is indispensable for handheld laser-induced breakdown spectroscopy (LIBS) instruments. We developed a passive, Q-switched pulsed, Nd:YAG laser system with small size and low cost. The maximum pulse energy of the laser was 10 mJ and the pulse duration was <2 ns. The peak power was >5 MW. The laser exhibited very high stability without any cooling system and its relative standard deviation of the pulse energy was <0.2 % . The laser was also used as a light source of LIBS to measure the concentrations of Cr, Cu, Mn, and Ni in alloys. The experimental results show that the determination coefficient of the calibration curves for these four elements is all better than 0.99. For its shorter pulse duration, the laser can decrease the plasma shield effect to improve the coupling of laser pulse and the target and stability of spectra intensity. The portable laser developed is a good laser source for handheld LIBS instruments.