Evapotranspiration represents one of the main parameters in the hydrological cycle. It is usually expressed by the term Reference evapotranspiration (ETo), that is affected by some meteorological parameters. This study aims to find the difference amount in reference evapotranspiration (ETo) between urban and suburban quarters in Karbala city. Study methodology includes selecting once urban area and four suburban quarters. Two methods of determining the reference evapotranspiration were applied. First, a direct method which measured reference evapotranspiration (ETo) at selected fields by using a hand-held device. Second, an indirect method was used Penman-Montieth equation. The findings showed that magnitudes of reference evapotranspiration (ETo) by Penman-Montieth equation are higher than the values measured by the direct method for urban and suburban quarters. Also, it was found that the absolute percentage of difference in the average amount of reference evapotranspiration (ETo) between urban and suburban quarters is 13% by using the direct method and 61% by using Penman-Montieth equation. Study conclusions are suburban area has higher magnitude of reference evapotranspiration (ETo) than urban quarter by using any of direct method and indirect method (Penman-Montieth equation).