As data rate of fiber optic communication systems increases to 10Gb/s or higher, chromatic dispersion (CD) of DWDM components becomes increasingly important. It has been shown that chromatic dispersion of passive components could have a detrimental effect on the performance of a 10Gb/s system. In this paper, we discuss chromatic dispersion of an important passive device: interleavers. To achieve better bandwidth efficiency, some system designers have started to evaluate 25GHz interleavers for their next generation products. However, the chromatic dispersion of an uncompensated 25 GHz interleave, regardless of its design, is 16 times larger than that of a 100 GHz interleaver of the same type. For example, if a 100GHz interleaver of certain design has an average CD of 40ps/nm, a 25GHz interleaver (uncompensated) of the same type would have a CD of 640ps/nm several interleavers available on the market. We show that chromatic dispersion of the interleavers is dominated by structural dispersion instead of material dispersion. The CD slopes and ripples of some interleavers can be reduced or completely compensated by innovative designs. We present an interleaver design with extremely small Cd and CD ripple. Finally, we present a 10Gb/s 160-channel transport application by using the low-CD 25GHz interleavers.