Abstract: Water resources in Southeastern Nigeria mainly depend on rainfall which is subject to great variability. Since, the wake of urbanization water use in the region has increase resulting in change in hydrological cycle. This study investigated the characteristics of oscillations that appear in the time series of annual rainfall amounts in Southeastern Nigeria with a view to predicting rainfall extremes. The analysis was carried out using the Autocorrelation Function Method. It was found that no significant trend was observed in all the climatic stations expect for Uyo within the periods of study (1982-2005). A general increase in annual rainfall amount was identified in almost all the stations from 1980 up to the end of the 20th century followed by a gradual decline or steady slope in the trend line of rainfall amounts. The study showed that highest rainfall amounts were mostly recorded between 1995 and 1997. From the correlogram analysis, a sequence of 4 years (Onitsha), 4, 6 and 15 years (Owerri), 5 years (Enugu), 3 years (Port-Harcourt), 1 year (Uyo), 10 years (Calabar), 1 year (Ikom) and 8 years (Ogoja) periodicities in cycles of high rainfall were determined in the study area. Cycles in rainfall deficiencies on the other hand yielded periodicities sequence of 10 and 11 years (Onitsha), 8 and 14 years (Owerri), 14 years (Enugu), 4, 7 and 10 years (Port-Harcourt), 12 years (Uyo), 12 years (Calabar), 3 years (Ikom) and 3 years (Ogoja). From the sequence of periodicities of cycles for rainfall deficiencies over Southeastern Nigerian similarities was observed between Uyo and Calabar and between Ikom and Ogoja pointing to the unique physical factors controlling the rainfall of these areas. Finally, results of the analysis are expected to provide information that would be helpful in formulating policies for mitigating flooding and drought in the region.