The most common destructive effect for fiber optical transmission systems (FOTS) is chromatic dispersion (CD). It increases with the increase of FOTS transmission distance and/or bitrate. Even if prevention activities for CD compensation are applied, wavelength division multiplexed (WDM) transmission systems still suffers from destructive effects of CD due to the fact that its value varies for each channel. Difference of dispersion value in each WDM channel can be compensated by compensating chromatic dispersion slope (CDSL). When CD and/or CDSL are compensated in WDM FOTS transmission system, it can significantly improve bit error ratio (BER) of each channel by reducing errors due to intersymbol interference (ISI). In this paper authors demonstrate dispersion slope compensation methods for 16-channel 40 Gbit/s per channel WDM C-band passive optical network (PON) transmission systems with non-return-to-zero (NRZ) and return-to-zero (RZ) line codes by using widely deployed ITU-T G.652 and G.655 optical fibers. Like CD compensation CDSL also can be compensated using two main methods - dispersion compensation fiber (DCF) and fiber Bragg grating (FBG). Main goal of this paper is to find out how does the chromatic dispersion slope compensation affect the performance of 100 GHz spaced 16-channel WDM-PON transmission system operating at 40 Gbit/s bitrate and determine the most suitable dispersion slope compensation method.