Nonadiabatic effects caused by lumped amplifiers in fiber soliton transmission systems are reduced by the use of dispersion-decreasing fibers between amplifiers. As a practical application, we consider a stepwise dispersion-decreasing fiber with M steps and show that the increase in M is almost equivalent to the reduction of amplifier spacing, Z(a), to Z(a)/M in reducing collision-induced jitters in soliton-based wavelength-division multiplexing systems.