Using bioinformatics analysis, we found some mature human miRNAs containing G-rich sequences with four G-tracts that had a high probability of forming G-quadruplex structures. Here, we chose G-rich miR-1587 as a model to characterize the function and regulation of miRNAs. Using electrospray ionization mass spectrometry, magnetic resonance imaging, circular dichroism spectrometry, we had confirmed that miR-1587 folded into a stable parallel G-quadruplex structure. By microarray, Q-RT-PCR and 3'UTR luciferase assay, TAGLN, an early marker of smooth muscle differentiation and tumor suppressor, was identified as a target gene of miR-1587, thus providing a direct target to study miR-1587 functions. We identified three aspects of miR-1587 regulation: 1) KCl induced miR-1587 G-quadruplex formation, reducing the interaction between miR-1587 and the target gene, and inhibiting miR-1587 function; 2) pseudopalmatine ligand further inhibited miR-1587 binding to TAGLN mRNA, which disrupted its function and increased the TAGLN expression; 3) the addition of TMPyP4 ligand interfered G-quadruplex formation, and significantly enhanced miR-1587 regulation of TAGLN expression. This study has revealed the possibility of using the G-quadruplex structure as a strategy to regulate miR-1587 function, showing potential for the development of up- and downregulation of mature G-rich microRNA function by modulating its G-quadruplex and using small molecules.