Diversity of root growth and accumulation of organic acids in Zn-inefficient and Zn-efficient rice genotypes under bicarbonate treatment can be an ecological strategy for plants grown on calcareous soils with low Zn availability. In this study, the effects of bicarbonate on root and shoot fresh and dry weight, root length, number of roots per plant and the accumulation of malate and citrate on four genotypes of rice (Oryza sativa L.) were examined. Two genotypes, Pokkali (Zn-efficient) and IR26 (Zn-inefficient), from IRRI were used as known cultivars for Zn efficiency and two genotypes from Iran (Shafagh and Domsiah) were examined for Zn efficiency. The results indicated that the one of Iranian cultivars, Shafagh, was a Zn-efficient and Domsiah (local variety) was Zn-inefficient. Results showed that bicarbonate significantly decreased the growth of roots in the Zn-inefficient genotypes but induced their growth in the Zn-efficient genotypes particularly after 8 days of treatment. The accumulation of malate and citrate were greater in Zn-inefficient genotypes, as compared with the Zn-efficient genotypes. We conclude that root characteristics and the accumulation of organic acids can be used in rice genotypes for screening Zn efficiency under bicarbonate treatment.