Abstract. Although knowledge of the physical state of aerosol particles is essential to understand atmospheric chemistry model and measurements, information on the viscosity and physical state of aerosol particles consisting of organic and inorganic salts are still rare. Herein, we quantified viscosities at 293 ± 1 K upon dehydration for the binary systems, sucrose/H2O and ammonium sulfate (AS)/H2O, and the ternary systems, sucrose/AS/H2O for organic-to-inorganic dry mass ratios (OIRs) = 4 : 1, 1 : 1, and 1 : 4. For binary systems, the viscosity of sucrose/H2O particles gradually increased from ~6 × 10−1 to > ~1 × 108 Pa‧s when the relative humidity (RH) decreased from ~83 % to ~24 %, which agrees with previous studies. The viscosity of AS/H2O particles remained in the liquid state (< 102 Pa‧s) for RH > ~50 %, and for RH ≤ ~50 %, the particles showed viscosity of > ~1 × 1012 Pa‧s, corresponding to a solid state. For ternary systems, the viscosity of organic-rich particles (OIR = 4 : 1) gradually increased from ~4 × 10−2 to ~1 × 108 Pa‧s for a RH decrease from ~80 % to ~18 %, similar to the sucrose/H2O particles. In the particles for OIR = 1 : 1, the viscosities ranged smaller than ~4 × 101 for RH > 34 %, and > ~1 × 108 Pa‧s at ~27 % RH. Compared to the organic-rich particles, in the inorganic-rich particles (OIR = 1 : 4), drastic enhancement in viscosity was observed as RH decreased; the viscosity enhanced approximately 8 orders of magnitude in RH from 43 % to 25 %. Based on viscosity data, all particles studied in this work were observed to exist as a liquid, semi-solid or solid depending on the RH. Furthermore, we compared the measured viscosities of ternary systems with OIRs of 4 : 1, 1 : 1, and 1 : 4 to the predicted viscosities using the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients Viscosity model (AIOMFAC-VISC) predictions with the Zdanovskii–Stokes–Robinson (ZSR)-style organic–inorganic mixing model, with excellent model–measurement agreement for all OIRs.