Field performance of rice allelopathic potential is indirectly regulated by the microbial flora in rhizosphere. The present study aimed to investigate the population dynamics of microbial flora and their functional diversities in the rhizospheres of rice seedlings of a range of rice varieties with varied allelopathic activity by employing agar plate bioassay, fumigation, as well as BIOLOG analysis. Rice cultivars significantly affected the microbial carbon content in their associated rhizospheres. The contents of microbial carbon were ranked in the decreasing order as cv. Iguape Cateto (441.0 mg•kg^-1) > IAC47 (389.7 mg•kg^-1) > PI312777 (333.2 mg•kg^-1) > Lemont (283.8 mg•kg^-1), with the nil-rice control soil of 129.3 mg•kg^-1. Similarly, the respiration rates of the soils were 1.404, 1.019, 0.671 and 0.488 μgC•g^-1•h^-1 for cv. PI312777, Iguape Cateto, IAC47 and Lemont, respectively. The respiration rate was only 0.304 μgC•g^-1•h^-1for the control soil. The microbial flora in the rhizospheric soils of different rice cultivars was dominated by bacteria (58.4%- 656%), followed by actinomycete (32.2%-39.4%) and fungi (2.2%-2.8%). BIOLOG analysis showed that the value of Average Well Color Development (AWCD) differed significantly among rice cultivars. It was always the highest in the rhizospheric soil of the strongly allelopathic rice cv. PI312777, and the lowest in the poorly allelopathic rice cv. Lemont. The AWCD values reached the maximum in all the sampled soils after 144 hours of incubation. The AWCD values from the rhizospheric soils of PI312777, IAC47, Iguape Cateto and Lemont were 1.89, 1.79, 1.60 and 1.43 times higher than that of the control soil. Principal Component Analysis (PCA) identified 3 principal component factors (PCF) in relation to carbon sources, explaining 70.1%, 11.3% and 7.0% of the variation respectively. Nineteen categories of carbon sources were significantly positively related to the 3 principal components. Phenolic acids, carbohydrates, amino acids and amides were significantly related to the principal component 1, phenolic acids, carbohydrates and fatty acids to the principal component 2, and carbohydrates and hydroxylic acids to the principal component 3. Amino acids and amides were the two main carbon sources separating the 3 principal component factors. In addition, the total microbial populations of rhizospheric soils were significantly positively correlated with AWCD, microbial biomass carbon, microbial respiration and Shannon index. There was a significant positive association between the total microbial population and the % inhibition on the root length of lettuce due to the differential allelopathic activities of the rice cultivars. These results suggest that changes in microbial population, activity and functional diversity in the rhizospheres are highly cultivar-dependent. These changes might play a role in governing the rice allelopathic activity in the field.