A straightforward wet chemical method has been applied for the fabrication of Yb2O3 nanoparticles (NPs) from ytterbium nitrate solution by using ammonium carbonate as precipitation agent. Effects of precursor molarity (0.1, 0.15 and 0.2 M), calcination temperature (800, 900 and 1000 degrees C) and time (2, 4 and 6 h) on average crystallite size (CS) of the NPs were statistically investigated by using Box-Behnken design. A simple and effective quadratic model was proposed for controlling the CS. The CS values were calculated by using Williamson Hall method (W-H) from X-Ray Diffraction (XRD) broadening data and found to be ranging between 13 and 26 nm. Agglomerated NPs morphologies and particle sizes were revealed by Field Emission Gun-Scanning Electron Microscopy (FEG-SEM). Fourier Transform Infrared (FTIR) spectrophotometry confirmed that as-received Yb-2(CO3)(3)xH(2)O powders were successfully transformed into Yb2O3 NPs with calcination. High-Resolution Transmission Electron Microscopy (HRTEM) results verified the average CS values. ANOVA analyses revealed that linear and squared terms of the production parameters were significantly related to the CS whereas interaction terms were insignificant with the confidence level of 95% (R-2 = 92.67%, R-2-adj = 87.17%). The calcination temperature had the highest impact on the average CS followed by the time and precursor molarity. Increasing calcination parameters resulted in bigger crystallites whereas increasing precursor molarity exhibited a critical supersaturation value (0.15 M) from which the average CS was decreased.