Currently, inputting mathematical formulas into a document using a PC requires more effort by users than inputting normal text. This fact inhibits the spreading of mathematical formulas as internet contents. We propose a method for predicting user’s inputs of mathematical formulas using an N-gram model: a popular probabilistic language model in natural language processing. Mathematical formulas are usually presented in hierarchical structure. Therefore, our method incorporates hierarchical information of mathematical formulas to create a prediction model. We try to achieve high prediction accuracy of inputting characters for mathematical formulas.