MicroRNAs (miRNAs) are single-stranded, non-coding small RNAs that usually function as posttranscriptional negative regulators by base pairing to target genes. They are pivotal to plant development. MiR396 is conserved among plant species and is predicted to target GRF (growth-regulating factor) genes in Arabidopsis. Here, overexpression of ath-miR396 in tobacco reduced the levels of three NtGRF-like genes containing an miR396 match site. Furthermore, its elevated expression resulted in a small, narrow leaf phenotype similar to that found with the Arabidopsis grf1grf2grf3 triple mutant. We also demonstrated that 35S:MIR396a transgenic plants were defective in the four whorls of floral organs. These results provide a link between the miR396-mediated regulatory pathway of NtGRF-like gene expression and the developmental processes for leaves and flowers in tobacco.