The diameter distribution is one of the most powerful tools for depicting the properties of a stand. Diameter has generally strong correlations with other important stand variables including basal area, volume, etc. Quantification of the diameter distribution and its relationship to site, stand composition, age, and density is often valuable for both economic and biological purposes. In this case, the diameter distribution of stands should be determined with appropriate probability functions for all these purposes firstly. In this paper, we consider four probability density functions (Exponential, Exponential with two parameters, Weibull with two parameters and Weibull with three parameters) as diameter distribution models for Bornmullerian fir (Abies nordmanniana subsp. bornmulleriana) in mixed coniferous stands.