Background <p>This study aims to assess PM_2.5-attributable five chronic diseases burden in BRICS-plus over 1990–2021, identify key driving factors, and provide evidence for targeted air quality and public health policies.</p> Methods <p>We analyzed the PM_2.5-attributable burden of ischemic heart disease, stroke, type 2 diabetes mellitus (T2DM), chronic obstructive pulmonary disease (COPD), and tracheal/bronchus/lung cancer for both ambient PM_2.5 and household air pollution from solid fuel combustion (HAP). Decomposition analysis (aging, population, epidemiological change) and population attributable fractions (PAFs) were used to explore burden drivers and preventable disease burden.</p> Results <p>Ambient PM_2.5-attributable chronic disease burdens showed an upward trend in most BRICS-plus, particularly of T2DM burden in China (from 14.10 [6.17,25.82] to 134.47 [72.81,213.96] from 1990 to 2021) and India (from 15.41 [7.58,27.09] to 102.53 [53.86,161.27] from 1990 to 2021). HAP-attributable showed increases trend in India and Ethiopia. Population has made a consistent positive contribution to the evolving disease burdens. Ethiopia showing the highest HAP-PAFs (COPD: 60.83%, stroke: 39.58%). Egypt and Saudi Arabia showed highest ambient PM_2.5-PAF.</p> Conclusions <p>Overall, ambient PM_2.5 has become an important contributor to chronic disease burdens (notably in China and India), while HAP-attributable burdens generally declined except in India and Ethiopia. Population contributed positively to five disease burdens, aging and epidemiological changes notable country differences. Reducing PM_2.5 and HAP to TMREL significantly alleviated disease burdens (particularly COPD). BRICS-plus countries should address ambient PM_2.5and HAP, population growth and protect vulnerable groups to mitigate the long‑term PM_2.5-related disease burdens.</p>