The magnetic and structural properties of amorphous Fe40Ni39Mo4B18 alloy which is a precursor of new nanocrystalline material have been investigated. Differential scanning calorimetry (DSC) and the temperature dependence of resistivity were used to determine the structural stability and the crystallization temperatures. It was shown that amorphous FeNiMoB alloy crystallizes in two stages. Firstly at the temperature 360 degreesC, the FeNi phase appears, secondly at about 450 degreesC FeNiMo borides crystallize. The temperature dependence of the initial susceptibility describes the evolution of the magnetic properties in an amorphous state as well as during nano crystallization; the Curie temperature was found to be 327 degreesC. The magnetic after-effect (MAE) was also studied. The MAE spectrum consists of a thermally activated peak at 200 degreesC. The activation energy spectra (AES) were determined from the MAE by means of a computer analysis.