The structure, internal friction (IF) behavior, resistivity and magnetostriction property of Fe-18Ga alloy were systematically analyzed in this investigation. In the IF spectra of Fe-18Ga alloy covered from room temperature (RT) to 800 degrees C, a prominent IF peak (labeled as P-tr peak) was observed in the high temperature range 530 degrees C-690 degrees C besides the reported IF peak related with grain boundary relaxation in the moderate temperature range 400 degrees C-530 degrees C. The peak position of Ptr peak hardly changes with measuring frequency, implying that its mechanism is most possibly related with phase transition. Considering from the wide peak shape, Ptr peak can be decomposed into two components: the lower temperature Pal peak located around 530 degrees C-605 degrees C and the higher temperature P-tr2 peak located around 605 degrees C-690 degrees C. Combined with calculated phase diagram, resistivity and magnetostriction analysis, the mechanism of Ptr peak was suggested to originate from the order-disorder phase transition related with Ga atom distribution in Fe-18Ga alloy: P-tr1 peak was ascribed to D0(3) -> B2 transition and P-tr2 peak was ascribed to B2 -> A2 transition, respectively. (C) 2018 Elsevier B.V. All rights reserved.