The accurate knowledge of radio refractive and water vapour density of the troposphere is important in the planning, budgeting and designing of transmission and reception of radiowave signals on earth-space path. Hence, there is the need to adopt more precise techniques to analyze the seasonal variation of refractivity and water vapour density over Nigeria. The seasonal variation of refractivity and water vapour density was studied using thirty-nine years meteorological data for forty-eight (48) stations over Nigeria. The forty-eight stations were grouped into nine vegetation and two major climates in Nigeria. Harmonic analysis approach was used in addition to the monthly mean computation. The results show that Forests zones values of refractivity and water vapour density are higher than Savannahs zones values. The refractivity value increases from about 281 N units at Sudarian Woodland in January to about 383.6 N units at Mangrove station in June. Water vapour density value increases from about 5.18 g/m3 at Brush and Thicket station in November to maximum value of about 22.36 g/m3 at Swamp Forest station in May. Results also show that over 80% variations in refractivity and over 70% variations in water vapour density are revealed in the first three harmonics at all the nine stations. The results indicate that the method of harmonic amplitudes and phases give a more analytical comparison between predictions model and observational data
