Measurements of the magnetomechanical coupling constant, k, and the &Dgr;E effect have been made on Fe71Co9B20glassy ribbons quenched by a centrifugal spinning method. An X‐ray check of the ribbons showed no trace of crystallinity. The maximum k and &Dgr;E effect were 0.81 and more than 2.2, respectively, obtained after a field anneal of 20 kOe parallel to the width of the ribbon at 384±5°C for 15 min. This relative change in modulus is the largest known.