Abstract: While the most challenge research scopes of geodesy/surveying science are to identify the highly accurate three-Dimensional (3D) coordinates (φ, λ, h/H), the vertical positioning (h/H) are the most crucial for many applications in civil engineering projects. These projects require to convert the Ellipsoidal height (h) [observed by the Global Positioning System (GPS)] to orthometric Height (H) [observed by traditional field survey techniques such as spirit levelling]. The difference between the ellipsoidal height (h) and orthometric Height (H) called the geoid undulation or geoidal height (N). The Global Geopotential Model (GGM) is a model that is being represented by the spherical harmonic coefficient that defines the potential of gravitational in the spectral domain. Lately several GGM have been developed based on the accurate data collected by the different satellite missions. Due to the importance of Egypt location, there are many efforts for applying (as international projects) and/or modifying (as researches studies) several of these GGMs. Also, since, Egypt has area up to one million km² and due to the limited input data for different GGMs, therefore ,the accuracy of the GGMs are low. So, it’s expected that the undulation values (N) will be different when using different GGMs. This paper aim to study the relation between the undulation values (N) using most common eight GGMs. The study will be on regular points distribution (346 point) between latitudes φ [22°N, 31°N] and between longitudes λ [26°E, 36°E] which cover whole Egypt territories. Generally, the maximum (N) value reach 21.47 m at [29.5°N, 33.5°E], the minimum value reach 7.23 m at [22.5°N, 36°E], the maximum difference of N calculated using deferent GGM reach 6.08 m at [28.5° N, 34°E] and the minimum difference reach 0.36 m at [26°N, 27°E].