Abstract: The effects of Cr on the electrical properties of the(Co,Ta)-doped SnO₂ varistors were investigated.The breakdown voltag e of the SnO₂ based varistors increases from 206V/mm to 493V/mm,the relative dielectric constant decreases significantly from 1968to 498at 1kHz with Cr₂ O₃ concentra-tion increasing from 0to 0.15mol%.Measurement of the barrier height at g rain boundary reveal that the reason why breakdown voltage resistivity increases and relative die lectric constant decreases is the significant decrease of the SnO₂ grain size with Cr₂ O₃ concentration increasing from 0to 0.15mol%.The origin for the deduction of SnO₂ grain size with Cr₂ O₃ concentration increasing is explained.The 0.15mol% Cr₂ O₃-doped SnO₂ varistor with breakdown voltage of 493V/mm and larger nonlinear coefficient (α=24) is a candidate used in the high voltage protection system.