Cut Fe 4 0 Ni 4 0 (Si+B) 1 9 Mo 1 - 2 ribbons were annealed for 2h at various temperatures between 350 o C and 600 o C. XRD and Mossbauer effect spectroscopy (ME) measurements were then performed on all of the ribbons. The magnetic properties of several ribbons were measured using a vibrating sample magnetometer (VSM). A differential thermal analysis scan (over the range 20-800 o C) of the as-cast ribbon showed two phase transitions; the first at 454 o C and the second at 525 o C. Both the XRD and ME spectra of the as cast, the 350 o C and 400 o C annealed ribbons showed that they were amorphous. The ME spectra of the 450 o C, 475 o C and 500 o C annealed ribbons showed that these ribbons contained α-Fe, α-Fe(Si) and t-Fe 2 B nanocrystallites. For the ribbons annealed above 550 o C, crystallites of t-Fe 2 B, t-Fe 3 B, t-Fe 5 SiB 2 and FCC-FeNi appeared, with the α-Fe and α-Fe(Si) crystallites disappearing. The sextets of all of the Fe compounds appeared in the ME spectra of the 525 o C annealed ribbon. The VSM measurements supported the picture of a two-stage phase transitions; amorphous phase->a nanocrystalline phase (Fe-containing nanocrystallites in an amorphous matrix) at 454 o C and then a second transition, the nanocrystalline phase->a disordered alloy containing Fe-B and Fe-Ni crystallites at 525 o C.