Objective: To investigate the effects of hesperetin on fine particulate matter (PM_2.5) induced apoptosis in H9c2 cells and related mechanisms. Methods: H9c2 cells were divided into 4 groups: control group (cells were cultured without intervention), PM_2.5 group (cells were treated with 800 µg/ml PM_2.5), hesperetin group (H group, cells were treated by 40 µmol/L hesperetin for 1 h at 37 ℃), and hesperetin+PM_2.5 group (H+PM_2.5 group, cells were pretreated with hesperetin before PM_2.5 treatment). Cells were cultured for corresponding interval. Apoptotic cells were detected by Annexin Ⅴ-FITC/PI apoptosis detection kit and Hoechst staining. The intracellular reactive oxygen species (ROS) levels were measured by DCFH-DA Fluorescence Probe and mitochondrial membrane potential (MMP) was detected with JC-1 staining, respectively in these groups. Apoptotic related protein and phosphorylated MAPK expression levels were determined by Western blot. Results: (1) Flow cytometry results showed that the apoptosis rate of PM_2.5 group ((48.94±3.20)%) was significantly higher than that of control group ((8.13±1.40)%, P<0.01), which was significantly reduced in H+PM_2.5 group ((34.80±2.21)%) (P=0.003 2 vs. PM_2.5 group, P<0.01 vs. control group). The number of Hoechst 33258 positive apoptotic cells was distinctly less in H+PM_2.5 group than in PM_2.5 group. (2) The ROS levels was significantly higher in PM_2.5 group ((49.69±5.05)%) than in control group (10.57±1.33)%, P<0.01), which was significantly reduced in H+PM_2.5 group ((35.08±3.90)%) (P=0.000 2 vs. PM_2.5 group, P<0.01 vs. control group). (3) Green fluorescence indicating the JC-1 monomer form, which represented MMP loss of H9c2 cells, was significantly higher in PM_2.5 group ((20.28±4.69)%) than in control group ((10.50±2.72)%, P<0.01), which was significantly decreased in H+PM_2.5 group ((13.41±2.89)%) (P<0.01 vs. PM_2.5 group, P=0.029 4 vs. control group). (4) The expression levels of Bcl-2 protein of H9c2 cells was lower in PM_2.5 group ((76.94±4.52)%) than in control group (100%, P=0.000 9), which was significantly upregulated in H+PM_2.5 group ((92.95±6.82)%) (P=0.027 5 vs. PM_2.5 group, P=0.15 vs. control group). The expression levels of cleaved caspase-3 protein of H9c2 cells was significantly higher in PM₂.5 group ((243.98±17.94)%) than in control group (100%, P=0.000 2), which was significantly downregulated in H+PM_2.5 group ((200.45±4.31)%) (P=0.015 vs. PM_2.5 group, P<0.01 vs. control group). (5) The expression levels of phosphorylated p38 MAPK protein of H9c2 cells was higher in PM_2.5 group ((118.90±4.78)%) than in control group(100%, P=0.002 7), which could be significantly downregulated in H+PM_2.5 group ((103.30±1.27)%) (P=0.01 vs. PM_2.5 group, P=0.05 vs. control group). The expression levels of phosphorylated ERK protein of H9c2 cells was higher in PM_2.5 group ((163.50±4.98)%) than in control group (100%, P<0.01), which was significantly downregulated in H+PM_2.5 group ((139.10±2.72)%) (P=0.001 6 vs. PM_2.5 group, P<0.01 vs. control group). Conclusions Hesperetin protects H9c2 cells from PM_2.5 stimulation through reducing oxidative stress and protecting mitochondrial function, regulating the expression of apoptotic associated proteins as well as MAPK signal pathway, thus inhibiting H9c2 cells apoptosis.