Although it is known that desert dust exacerbates allergic diseases, how it affects the onset of autoimmune diseases is unclear. No epidemiological investigations or animal experiments have been conducted so far to elucidate the effects of desert dust on autoimmune diseases. Here, we focused on particulate matter, such Asian sand dust (ASD) that has been known to cause adverse health effects in East Asian countries, and conducted animal experiments to examine how ASD influences type 1 diabetes (T1D), an autoimmune disease. An ASD suspension was intratracheally administered into NOD mice, which spontaneously develop T1D, for 4 times at 2-week intervals. Subsequently, the incidence of cyclophosphamide (CY)-induced diabetes was examined, which was then quantified using adoptive splenocyte-transfer assays. Kaplan-Meier curves of the cumulative T1D incidence were compared using the log-rank test, and unpaired two-tailed t tests were used for comparing the other data. We observed that ASD administration delayed T1D, and adoptive splenocytes derived from ASD-administered donor NOD mice also delayed the onset of T1D in recipient NOD mice. We further found that ASD increases concanavalin A-induced IFN-γ production and decreases regulatory T cells. Consequently, ASD suppresses the onset of T1D, activates spleen cells, and affects T-cell differentiation.