In this study precipitation, drought and erosivity indices and arid periods of Ankara Yenimahalle Guvenc Basin were determined. Fournier Precipitation Index and Bagnouls-Gaussen Drought Index were calculated using rainfall data that were measured among 1984–2008 in the basin and temperature data that were taken from Turkish State Meteorological Service. Precipitation index was 63.8 and defined as low level, drought index was 112.6 and defined as dry level, erosivity index depending on rainfall and temperature was 5.3 and defined as medium level. Arid periods were determined by using rainfall and temperature data of the basin. The long term drought was occurred in 2002, the short term drought occurred in 1998 and the most severe drought occurred in August in 2008 in the basin.