An optical voltage sensor is proposed which uses one single bismuth si licate (Bi₁₂SiO₂₀, BSO) crystal grown by hydrothermal method.The voltage sensing unit is only comp osed of one block of BSO crystal and two prism polarizers.Experimental results demonstrate th at the used BSO crystal sample exhibits obvious linear electro-optic Pockels effect,and can be used for the measurement of alternating voltage.By use of the inherent natural optical activity in the B SO crystal, monotonous and linear voltage measurement ranges of the proposed voltage sensor are larger than those of the conventional voltage sensors using electro-optic crystals without optical activity. The size of the used BSO crystal sample is 6.0mm×4.0mm×2.9mm³.The angle, through which the plane-of-vibration rotates in the BSO crystal due to its optical activity,is a bout 132° for light wavelength of 633nm.The measurand voltage is the alternating voltage with indu strial frequency of 50Hz,and is monotonously and nonlinearly measured in the range of 108-1300V (root-mean-square amplitude).The output voltage of the sensor is still monotonously changed with measured voltage when the corresponding electro-optic phase retardation reache s 2π.In addition,under the application of a proper stress-induced birefringence in the BSO crystal,the ou tput voltage is linearly changed with measured voltage in a certain voltage range,e.g.,900V,c orresponding voltage measurement sensitivity is 0.0276mV/V and nonlinear error is less than 3.1%.