The solid-state diffusion reaction between Fe and Al was studied using bulk diffusion couples in the temperature range 450°C to 600°C for annealing durations up to 240 h. The Al-rich intermetallic phase Fe2Al5 formed in the diffusion zone at all annealing temperatures. However, for diffusion couples annealed at and above 600°C, additional intermetallic phases Fe3Al, FeAl, and FeAl2 appeared in the diffusion zone. The existence of these phases at and below 640°C and the composition range of their existence were investigated, and these results provided better insight into the existing Fe-Al phase diagram. It was observed that Fe2Al5 is the dominant phase in the diffusion zone, and the formation of this phase was rationalized based on the modified effective heat of formation model. Both kinetic and diffusion parameters were evaluated for Fe2Al5, and the activation energy for interdiffusion of this phase was found to be 146.8 kJ/mol; these results were compared with previously published work.