The present study has been accomplished in two parts i.e. the development of ARIMA and ARIMAX models for mustard yield forecasting in Bhiwani, Fatehabad, Hisar and Sirsa districts of Haryana. The ARIMA models have been fitted using mustard yield data for the period 1980-81 to 2011-12 of Bhiwani, Hisar and Sirsa districts (Fatehabad from 1997-98 to 2011-12). However, the fortnightly weather data from 1980-81 to 2016-17have been utilized as input for ARIMAX model building. The validity of fitted models have been checked for subsequent years i.e.2012-13 to 2016-17, not included in the development of the models. The ARIMAX models performed well with lower error metrics as compared to the ARIMA models in all time regimes.