The objective of this research is to study the collapse mechanism of stearic acid monolayer at surface pressure beyond its equilibrium spreading pressure. A film balance system and a transmission electron microscope were utilized to investigate the constant surface pressure relaxation kinetics and the microstructures of the collapsed monolayer, respectively. And the nucleation-growth model proposed by Vollhardt et al, was applied to simulate the constant surface pressure relaxation behavior. By a non-linear regression method proposed herein, we confirmed that the final surface area is a sensitive parameter in determining the best fit value of time exponent, which represents a specific nucleation-growth mechanism, and the best fit value of time exponent claimed by Vollhardt et al, utilizing a linear regression method is actually incorrect. Our electron microscopy observations illustrated that the collapse structure of stearic acid monolayer is terrace-like and irregular in shape. This result of morphological study implied that the geometric shape of the collapse structure is not an important factor in determining collapse rate. This statement correlates well to the fact disclosed by the present non-linear regression studies, i.e., there is no optimum value of time exponent can be determined by analyzing the relaxation data alone. In order to predict the overall transformation rate constant for a monolayer with various surface pressure, a simple empirical equation describing the relationship between rate constant and surface pressure of stearic acid films was also established for the case of time exponent equal to 2.0.