Objective To understand the distribution and antimicrobial resistance changes of bacteria isolated from pleural and peritoneal effusion in Hunan Province, and provide reference for correct clinical diagnosis and rational antimicrobial use. Methods Data reported by member units of Hunan Provincial Antimicrobial Resistance Survei-llance System from 2012 to 2021 were collected. Bacteria antimicrobial resistance surveillance method was implemented according to technical scheme of China Antimicrobial Resistance Surveillance System (CARSS), and WHONET 5.6 software was used to analyze the data of bacteria isolated from pleural and peritoneal effusion as well as antimicrobial susceptibility testing results. Results From 2012 to 2021, a total of 28 934 bacterial strains were isolated from specimens of pleural and peritoneal effusions from member units of Hunan Provincial Antimicrobial Resistance Surveillance System, with 5 752 strains from pleural effusion and 23 182 from peritoneal effusion. The top five bacteria isolated from pleural effusion were Escherichia coli (n=907, 15.8%), Staphylococcus aureus (n=535, 9.3%), Klebsiella pneumoniae (n=369, 6.4%), Staphylococcus epidermidis (n=452, 7.9%), and Staphylococcus haemolyticus (n=285, 5.0%). The detection rate of methicillin-resistant Staphylococcus aureus (MR-SA) from pleural effusion was 24.3%-39.2%, and that of methicillin-resistant coagulase negative Staphylococcus (MRCNS) was 58.8%-77.1%. The top five bacteria isolated from peritoneal effusion were Escherichia coli (n=8 264, 35.6%), Klebsiella pneumoniae (n=2 074, 9.0%), Enterococcus faecium (n=1 458, 6.3%), Staphylococcus epidermidis (n=1 383, 6.0%), and Pseudomonas aeruginosa (n=1 152, 5.0%). The detection rate of MRSA from peritoneal effusion was 22.1%-52.4%, which presented a decreasing trend (P=0.004). The detection rate of MRCNS was 60.4%-79.4%. The resistance rates of Enterobacterales from peritoneal effusion to cefazolin, cefuroxime, ceftriaxone and cefepime all showed decreasing trends (all P < 0.05). Vancomycin-, linezo-lid-, and teicoplanin-resistant Staphylococcus strains were not found in pleural and peritoneal effusions. The resis-tance rates of Enterococcus faecium to most tested antimicrobial agents were higher than those of Enterococcus faecalis. The resistance rates of Enterobacterales to imipenem and meropenem were ≤ 8.5%. The resistance rates of non-fermentative Gram-negative bacilli to imipenem and meropenem were ≤ 43.3%. Conclusion The data structure of Hunan Antimicrobial Resistance Surveillance System for pleural and peritoneal effusions from 2012 to 2021 is relatively complete. The constituent and antimicrobial susceptibility of isolated pathogenic bacteria vary in different years.