One of the key problems of swarm robotics is how the mobile robots can navigate accurately in a given environment. To achieve this, the mobile robots need to accurately determine where they are globally, or relative to other robots and landmarks. This paper is going to be an investigation of the Monte Carlo Localization algorithm in an environment containing 3 anchors. In addition, an alternative modification is suggested to this localization algorithm to improve the localization performance. An experiment is devised to assess different aspects of localization performances of these algorithms. With the experimental results, a quantitative analysis of performance figures are compared and analyzed.