Geoid undulation has been determined for Nigeria in order to demonstrate its relationship with topography and the dynamic structure of the Earth’s interior. Spherical harmonic expansion using the Earth Gravitational Model 2008 (EGM2008) referenced to the WGS84 (World Geodetic System 1984) with coefficients extending to degree 2190 and order 2159 was found suitable for the determination of geoid undulation. The results from the analysis show that the Nigerian geoid undulations are positive and show overall good correlation with topography. The internal origin of the geoid undulation is attributed to excess mass beneath the ellipsoid. This internal mass distribution extend deep into the mantle. The highest geoid undulations are centered over the North central region of Nigeria with relatively lower values confined to the Nigerian sedimentary basins. The lowest geoid undulation values are within the oceanic areas.