Reliability assessment of component based software system plays a vital role in developing quality software systems using component based development methodology. This can be achieved by Monte Carlo Simulation Method of reliability prediction when software system complexity makes the formulation of exact models essentially impossible. The characteristics of the Monte Carlo method make it ideal for estimating the reliability of component based software systems. Unlike many other mathematical models, software system complexity is irrelevant to the method. Not only can the structure of the software system be dynamic, but the precise structure of the software system need not even be known. Instead, software system components need only be tested for failure during operation, which ensures that software components which are used more often contribute proportionally more to the overall software system reliability estimate. This paper presents a novel Monte Carlo Simulation method for assessing the reliability of component based software systems.