The Curie temperature, Tc, crystallization temperature, Tx, anisotropy field, Ha, magnetomechanical coupling factor, K33, and magnetostriction have been measured as a function of nickel concentration in the metallic glass, Fe80-xNixB15Si5(x = 0, 10, 15, 20 and 40). The Curie temperature exhibits an absolute maximum at approximately 20 a/o Ni. This maximum is reflected in the values of Haas a function of Ni content. Magnetostriction measurements indicate that the saturation magnetostriction decreases only slightly with increasing Ni content between 0 and 20 a/o Ni, and then decreases rapidly between 20 and 40 a/o Ni. The maximum achievable magnetomechanical coupling factor as a function of Ni content decreases approximately linearly with increasing a/o Ni (0.006 per a/o Ni) and is sensitive to the relative magnitudes of the uniaxial anisotropy energy and saturation magnetostriction.