Wireless passive devices based on surface acoustic wave (SAW) technology are the firstly selected sensors in extreme conditions, and high temperature stability of piezoelectric substrates is the key factor limiting the performance of SAW devices. Langatate (LGT) crystal is an ideal high temperature piezoelectric substrate for SAW devices due to high resistivity and stability. The high temperature resistivity of pure LGT and aluminum- doped langatate (LGAT) crystals in oxygen, nitrogen and argon atmosphere were characterized, and the high temperature full matrix material coefficient of pure LGT crystal was characterized by ultrasonic resonance spectroscopy (RUS) technology. The results show that conductive behavior of LGT crystal under high temperature were significantly varied when tested in different atmospheres. The pure LGT crystal in nitrogen has the highest resistivity in the temperature range of 400-525 ℃, and in argon has highest resistivity between 525 ℃ and 700 ℃, with resistivity up to 2.05×10⁶ Ω·cm at 700 ℃. However, LGAT crystal in nitrogen has the highest resistivity in the whole test temperature range, with a resistivity of 1.12×10⁶ Ω·cm at 700 ℃, compared to pure LGT crystal. The elastic and piezoelectric properties of LGT crystal are very stable from room temperature to 400 ℃ according to RUS analysis results. As the temperature rises, the elastic coefficient decreases slightly, while the piezoelectric coefficient d₁₁ is remained almost unchanged. In conclusion, LGT crystal has very high resistivity and stability at high temperature so that it is suitable to be used as piezoelectric substrate for fabricating high temperature piezoelectric devices, shedding light on the design and fabrication of LGT-based high temperature piezoelectric devices.