Word prediction is the problem of guessing which words are likely to follow in a given segment of a text to help a user with disabilities. As the user enters each letters of the required word, the system displays a list of the most probable words that could appear in that position. In our research we designed and implemented a word predictor for the Persian language. Three standard performance metrics were used to evaluate the system including keystroke saving, the most important one. The system achieved 57.57% saving in keystrokes.