Abstract: MicroRNAs, which are types of non-coding RNAs 20-24 nt in length, regulate multiple physiological processes in plants. MicroRNA171 negatively targets the SCL gene family in plants, which causes altered branch architecture and other developmental changes in Arabidopsis, barley, and rice. It also regulates the metabolism of chlorophyll synthesis in Arabidopsis. However, the function of microRNA171 is unknown in other plant species. STTM171, the target mimic of miR171c, was designed based on the tobacco miR171c sequence and was overexpressed by a virus vector to investigate the function of miR171c in tobacco. The STTM171 overexpressed plants lost apical dominance and had several shoots. The expression of miR171c was decreased and the putative targeted genes TC134811 and TC127385, which encode SCL proteins, were upregulated in STTM171 overexpressed plants. These results indicate that the function of miR171c is likely conserved among tobacco and Arabidopsis, and it regulates target SCLs to affect developmental processes.