Amorphous Ni-B alloy films were prepared to electroplating from a bath containing (CH3)3NBH3 (trimethyla-mineborane TMAB). The films were lustrous. Boron codeposition in the films increased as the amount of TMAB in the bath was increased and as the current density was decreased. X-ray diffraction tests showed that films with boron codeposition of approximately 5wt% (equivalent to 22at%) or more were amorphous. This study showed the existence of a zone of pH values within which high boron codeposition is obtained. The maximum boron codeposition in the film prepared in this study was 6.24wt% (equivalent to 26.37at%).