Lake Tana is the biggest natural Lake in Ethiopia that provides a multiple of services to both the local, regional and national community. Understanding the Lake water balance using Precise estimates of its water balance terms including direct rainfall is the primary task to harness the services that it can offer in an effective, efficient and sustainable manner. Direct rainfall to that Lake Tana is one of the most important water balance terms of the Lake that needs precise estimate. This thesis tries to analysis the spatial and temporal variability of direct rainfall to the Lake and estimate the mean annual and mean monthly direct rainfall amount to the lake using sufficient data and appropriate methodologies. 30 years (1986-2015) monthly and mean annual data from 13 meteorological stations were collected and used to analyses the spatial and temporal variability. Spatial and statistical tools were used for data processing, analysis, and presentation. Five interpolation techniques: - Thiessen polygon, Spline, Isohytal, IDW, and Kriging were considered and their performances were assessed and compared using evaluation criteria. The results indicate that Isohytal method is slightly better than the other four methods and it is also easy to implement in a geographic information system (GIS) with Geostatic Analysis in ArcGIS. Further the analysis has shown that the mean annual direct rainfall to lake Tana is 1313.43mm with a standard deviation of 259.01. Besides, it has been seen that there is a significant spatial and temporal variability of direct rainfall on lake Tana. In terms of spatial variability, the Lake gets maximum direct rainfall in its southeastern part with an annual mean value of 1720mm and a minimum value in its northwest parts with an annual mean value of 860mm. In terms of Temporal variability maximum direct rainfall is estimated on July as 374.11mm with in Summer season and minimum is less than 12.3mm depth in the months of December, January, February and March in Winter.