Drought is one of the repetitive natural disasters that can be happened in each region. This event may damage the different parts of places severely. The most important factor in the occurrence of drought is lack of rainfall compared with the normal condition, also the evapotrairation adds to its intensity. Therefore, in this study, four proposed drought indices, which are based o precipitation and evapotrairation of reference data were used in scales of 3, 6 and 12 months (from winter) in Isfahan province. These indices are the standard values of« Ratio of Precipitation to Evapotrairation Index, RPEI», « Ratio of Precipitation to Precipitation Deficit Index RPPDI», « Precipitation Deficit Index, PDI» and « Evapotrairation Index, ETI». The Penman-Monteith FAO method, as a standard method, is used for calculating reference evapotrairation. In order to comparing the indices results, four indices are compared with the «Standardized Precipitation Index, SPI» in Similar scales. The results showed that the ETI, as a simple function of evapotrairation, has the least accommodation with SPI, based on events like drought, wet or normal conditions. Therefore, evapotrairation is an important factor affecting the Isfahan province, but way of including in the equation is very significant. Two indices (RPEI and RPPDI) have more accommodation with SPI. These two indices have low sensitivity with evapotrairation changes. PDI (the standardized difference between precipitation and evapotrairation), located in intermediate conditions. Frequency analysis of the RPE (Ratio of Precipitation to Evapotrairation) showed Daran and Khoorobiabanak have the wettest and driest climate between other stations. The result of zoning of relative percent drought frequency due to RPEI index showed that in general, in east, northeast and small portion regions of Isfahan province more droughts occurs, and thus these areas are more sensitive and need the most manipulating. Keywords: Drought index, evapotrairation, frequency analysis, Isfahan province