In this study, the isothermal reaction calorimetry of an Al/Ni multilayer material fabricated by an accumulative roll bonding method was performed using an isothermal calorimeter. An additive method was also devised to measure low-reactivity materials. Calorimetry results for several different numbers of cold-rolling passes indicated that the average calorific value of the reaction improved with an increase in the number of rolling passes, and the variance decreased. The calorific value of the deposited multilayer film, which had a uniform microstructure, was also measured. A comparison of the calorific values of the reaction between the powder and films showed that, although the films had a uniform structure, the average and variance were similar. These results experimentally confirmed that, although the multilayer film is extremely reactive at Al:Ni = 1:1 atomic composition ratio, the powder and film materials are equivalent with respect to the total heat generation of the high rolling pass condition.