Site diversity (SD) is an effective technique for mitigating rain attenuation in satellite communications, especially in regions where rainfall rates are high. Nigeria is characterised by the tropical climate, this implies that rainfall rates are generally high. This paper presents a study of the seasonal variation of site diversity technique in Nigeria at Ka-band frequency of 20 GHz. Rainfall data obtained from the Nigerian Meteorological Agency (NIMET) over a period of five years (2010 to 2014) were analysed to derive the one-minute rainfall rate distribution for four selected earth stations (University of Uyo, Uyo (UNIUYO); Akwa Ibom International Airport, Uyo (AKIA); Margaret Ekpo International Airport, Calabar (MEIA); and Port Harcourt International Airport, Port Harcourt (PHIA)) within the South-South Nigeria. The link parameters of Nigerian Communication Sattelite-1R (NigComSat-1R) were incorporated into the ITU-R model for rain attenuation to estimate the rain attenuation distribution through a seasonal cumulative distribution and percentage of outage time between 0.01 to 100%. Site diversity was implemented, taking University of Uyo as the reference site. The results obtained show that SD technique is most effective between the months of March and May and least effective between September and December.