Objective To investigate the role and underlying mechanisms of miR-34a/SIRT1 in intensive care unit acquired weakness (ICU-AW). Methods (1) C2C12 mouse skeletal muscle cells were induced to differentiate into myotubes, and were divided into two groups: model group [ICU-AW group, treated with lipopolysaccharides (LPS) for 12 hours] and normal control group (treated with the same amount of sterile water for 12 hours). Western blotting was used to detect the protein expression level of Muscle ring finger 1 (MuRF-1), atrophy gene 1 (Atrogin-1) and Sirtuin-1 (SIRT1). RT-qPCR was used to assess the mRNA expression level of microRNA-34a (miR-34a), MuRF-1, Atrogin-1 and SIRT1, and light microscope was used to observe the growth and differentiation of C2C12 skeletal muscle cells in each group. (2) ICU-AW cells were further subdivided into control group (treated with siRNA transfection agent intervention), Scra siRNA group (treated with transfection agent and non-specific siRNA), miR-34a siRNA group (treated with transfection agent and specific siRNA intervention), vehicle group (treated with agonist solvent dimethyl sulfoxide) and SRT1720 group (treated with SIRT1 agonist SRT1720). Western blotting was used to detect the protein expression level of SIRT1, Atrogin-1 and MuRF-1 in each group. RT-qPCR was used to detect the miR-34a and the mRNA expression level of SIRT1, Atrogin-1 and MuRF-1 in each group. (3) In addition, another group of ICU-AW cells were divided into control group (treated with siRNA transfection), miR-34a siRNA group (treated with transfection agent and specific siRNA intervention), miR-34a siRNA+vehicle group (treated with transfection agent, specific siRNA and Dimethyl sulfoxide intervention) and miR-34a siRNA+EX-527 group (treated with transfection agent, specific siRNA and SIRT1 inhibitor EX-527). Western blotting was used to detect the protein expression level of Atrogin-1 and MuRF-1. RT-qPCR was used to assess the mRNA expression level of Atrogin-1 and MuRF-1. Results Myotube differentiation was observed on the 4th day. Compared with control group, myotube atrophy was obvious in ICU-AW group. RT-qPCR and Western blotting results revealed that, compared with normal control group, in ICU-AW group, the mRNA and protein expression levels of Atrogin-1 and MuRF-1 significantly increased (P<0.05), and the expression level of miR-34a significantly increased (P<0.05), while the mRNA and protein expression levels of SIRT1 significantly decreased (P<0.05). RT-qPCR results showed that, compared with control group (treated with siRNA transfection agent intervention) and Scra siRNA group, the expression of miR-34a and mRNA expression of Atrogin-1 and MuRF-1 in miR-34a siRNA group significantly decreased (P<0.05), while the mRNA expression of SIRT1 significantly increased (P<0.05), meanwhile the protein expression of Atrogin-1 and MuRF-1 decreased significantly (P<0.01), and the protein expression of SIRT1 significantly increased (P<0.05). RT-qPCR results also showed that, compared with vehicle group, the mRNA expression of Atrogin-1 and MuRF-1 in SRT1720 group decreased significantly (P<0.05), while SIRT1 increased significantly (P<0.05). Western blotting results demonstrated that, compared with control group and Scra siRNA group, the protein expression of Atrogin-1 and MuRF-1 in miR-34a siRNA group decreased significantly (P<0.05), while SIRT1 increased significantly (P<0.05). RT-qPCR and Western blotting results indicated that, compared with miR-34a siRNA+vehicle group, the mRNA and protein expression of Atrogin-1 and MuRF-1 in miR-34a siRNA+EX-527 group increased significantly (P<0.05). Conclusion Overactivation of miR-34a in ICU-AW contributes to skeletal muscle atrophy by inhibiting the expression of SIRT1, which may play an important role in the pathogenesis of ICU-AW.