OBJECTIVE: To investigate the effects of lipopolysaccharide (LPS) and phytohaemagglutinin (PHA) on the level of microRNAs in mouse peripheral blood mononuclear cells (PBMCs). METHODS: The mouse PBMCs were cultured in vitro and stimulated with 100 ng/mL LPS for 1 hour or 2 hours and 2.5 μg/mL phytohaemagglutinin (PHA) for 2 hours or 4 hours, respectively. The levels of miR-9, miR-122-3p, miR-181d and miR-342-3p in both PBMCs and culture supernatants were determined by real-time quantitative PCR (qRT-PCR). RESULTS: The levels of miR-9, miR-122-3p, miR-181d and miR-342-3p in PBMCs and culture supernatants had no significant difference between blank control and LPS stimulation group, nor did between LPS stimulation 2 hours group and 1 hour group. The levels of miR-9, miR-122-3p and miR-342-3p in PBMCs and culture supernatant had no significant difference between blank control and PHA stimulation group, nor did between PHA stimulation 4 hours group and 2 hours group. However, compared with blank control, the expression of miR-181d significantly increased after PHA stimulation, while the time of stimulation did not affect the miR-181d level significantly. CONCLUSION: The stimulation of PHA could promote the expression and secretion of miR-181d in mouse PBMCs.