The back pain is the main common health problems on this decade because of the sitting for a long time tilted on the computer for working, studying or playing. The back problems are widely spread for different ages from young to old people. Last medical research demonstrates that sitting with the posture align can prevent and remedy many spine problems. In this paper, we propose ’SPLIGN’ which a posture monitoring system designed to help maintaining the good posture during sitting. The SPLIGN is a smart belt equipped with inertial sensors. A mobile and web applications are developed for monitoring and remind the user to correct posture. The proposed system is based on a detailed study of the machine learning algorithms in order to choose the best accurate algorithm for posture prediction. The main studied algorithms are Convolutional neural network (CNN), The K-nearest Neighbors (KNN), Support-vector machines (SVM), Decision tree classification, Random forest, Naive Bayes Classifier and Boosting algorithm. The test results demonstrate that The Random Forest algorithm has the best accuracy 99.67% compared to the other algorithms with appropriate processing time 67.7 ms for real time posture monitoring system.