Generalized anxiety and major depression disorders (MDD) are severe debilitating mood disorders whose etiology are not fully understood, but growing evidence indicates that microRNAs (miRNAs) might play a key role in their neuropathophysiological mechanisms. In the current study, we investigate the role of Lethal-7 (let-7d) miRNA and its direct target dopamine D3 receptor (D3R) gain-of-function, in the hippocampus, in preclinical models of anxiety and depression in mice. For this purpose, we have constructed a lentiviral vector carrying let-7d miRNA and its anxiolytic effect was investigated by employing the open-field (OF) and the elevated plus maze (EPM) tests. The anti-depressant activity was evaluated using the tail suspension and the forced-swim tests (TST & FST). Our results show that let-7d overexpression significantly improved the measures of anxiety in the OF and EPM tests. In addition, let-7d increased the mobility time in the TST and FST. Interestingly, gene expression interaction analysis shows that the D3R mRNA negatively correlates with let-7d expression. In a different set of experiments, we used a tetracycline-inducible (tet-off) lentiviral vector to overexpress D3R to assess its gain-of-function in the hippocampus on anxiety- and depression-like behaviors. In line, we found that in the absence of doxycycline, D3R produced a significant anxiogenic and depressant-like response. Most importantly, these effects were abrogated when mice were fed doxycycline in drinking water. Our results provide the first evidence for an anxiolytic and anti-depressant-like action of let-7d through a potential D3R target-mediated mechanism which might open new avenues for anxiolytic and anti-depressant therapies.