The polarization states of passively Q-switched microchip lasers were investigated by adopting different combinations of Yb:YAG, Cr,Ca:YAG crystals and ceramics. The results show that except for the random polarization oscillation of Yb:YAG/Cr,Ca:YAG all-ceramics combination, other three combinations including crystals exhibit linearly polarization. Highly efficient, nearly diffraction-limited beam quality, high peak power, sub-nanosecond passively Q-switched lasers were obtained for all combinations of Yb:YAG, Cr,Ca:YAG ceramics and crystals. The best laser performance was obtained with Yb:YAG/Cr,Ca:YAG crystals combination. The effect of polarization states on the laser performance was also addressed.