The purpose of this study is to estimate the probabilistic fatigue crack propagation models using the percentile of a random variable and to present the model fit for a probabilistic fatigue behavior in Mg-Al-Zn alloy. The probabilistic models proposed are probabilistic Paris-Erdogan model, probabilistic Walker model, probabilistic Forman model, and probabilistic modified Forman model. These models are prepared by applying a random variable to empirical fatigue crack propagation models such as Paris-Erdogan model, Walker model, Forman model, and modified Forman model.