Gaussian Process (GP) is a statistical tool where observations are considered normally distributed random variables. The technique uses previous observations and their covariances or similarities to analyze and predict future data. In this paper, the Gaussian random variable is the Received Signal Strength (RSS) between one anchor and one mobile station. In the training phase, the positions of anchor and mobile station together with the RSS between them are known. GP will use these data to predict the RSS at any other location of the mobile station. Experiment is conducted to validate the algorithm.