Gas nuclear transmutation effects in aluminum nitride were studied by the isotope tailoring method. In this method, nearly identical materials with two different radio-isotopes of nitrogen-14 (Al14N) and 15(Al15N) were prepared. The Al14N and Al15N specimens were irradiated in the JOYO fast reactor and the HFIR thermal reactor. The results were analyzed and compared to accumulated irradiation data from JMTR and JOYO. The data clearly shows the effects of gas nuclear transmutation on the linear dimension change.