D0-branes moving in a constant antisymmetric C field are found to be descri
bed by quantum mechanics of the supersymmetric matrix model with a similari
ty transformation. Sometimes this similarity transformation is singular or
ill-defined and cannot be ignored. As an example, when there are nonvanishi
ng C-ij components, we obtain the theory for Dp-branes which is effectively
the noncommutative super Yang-Mills theory. We also briefly discuss the ef
fects of other nonvanishing components such as C+ij and C-ijk. (C) 2000 Els
evier Science B.V. All rights reserved.