The present research aimed to investigate the effect of classroom interior design on the happiness and mental health of the students. Sixty girl students of ninth grade of Shiraz were selected in the academic year of 2015-16 by the random cluster sampling method; they were assigned to two groups of experiment and control during the three stages of pre-test, post-test and follow up through the Oxford Happiness and Mental Health Questionnaire. The results of variance analysis with the repeated measurements in the first stage showed that there is no significant relationship between the classroom interior design and the variables. However, a re-analysis of data without follow-up showed a significant increase in happiness, as well as the interior design has a significant effect on the mental health subscales (anxiety and physical signs) of the subjects. The interior design of the environment does affect the individuals within it, and it is possible to design suitable environments with regard to the environmental characteristics and the impact that the environment has on the students.
