SnO2 ceramics were co-doped with the aliovalent ions of CoO and Nb2O5 and the grain growth behavior of the SnO2 was investigated. When only CoO was doped, the grain growth exponent of SnO2 was 3. As the amount of Nb2O5 increased, the exponent changed from 3 to 2 when 0.505 mol% of Nb2O5 was added. The further addition of Nb2O5 changed the exponent from 2 to 3. When Nb2O5 content was 0.505 mol%, of which the grain growth exponent was 2, it is believed that an iso-electric point is formed without grain boundary segregation, since the respective space charges, generated by Nb5+ and Co3+ might compensate each other.