The primary objective is to investigate adverse effects of ambient particulate matter (PM) in various size on the incidence of prevalent autoimmune rheumatic diseases (AIRDs): Rheumatoid Arthritis (RA), Ankylosing Spondylitis (AS), and Systemic Lupus Erythematosus (SLE).We investigated 230,034 participants in three metropolitan cities of South Korea from the National Health Insurance Service-National Sample Cohort (NHIS-NSC). Starting from January 2010, subjects were followed up until the first event of prevalent AIRDs, death, or December 2013. 2008-2009 respective averages of PM2.5 (< 2.5μm) and PMcoarse (2.5μm to 10μm) were linked with participants' administrative district codes. Adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) were estimated using Cox regression analysis in one- and two-pollutant model.Adjusted for age, sex, region, and household income in two-pollutant model, RA incidence was positively associated with 10μg/m³ increment of PM2.5 (aHR = 1.74, 95% CI: 1.06-2.86), but not with PMcoarse (aHR = 1.27, 95% CI: 0.87-1.85). In one-pollutant model, an elevated incidence rate of RA was slightly attenuated (PM2.5 aHR = 1.61, 95% CI: 0.99-2.61; PMcoarse aHR = 1.13, 95% CI: 0.80-1.61), with marginal statistical significance of PM2.5. RA incidence was also higher in 4th quartile group of PM2.5 compared to 1st quartile group (aHR = 1.83, 95% CI: 1.07-3.11). No adverse effects of PM were found on AS or SLE in one- and two-pollutant models.Important components of PM10 associated with RA incidence were fine fractions (PM2.5), while no positive association was found between PM and AS or SLE.