Abstract: Determination of basin Instantaneous Unit Hydrograph (IUH) is important for design of hydraulic structures. Instantaneous Unit Hydrographs can be derived from rainfall runoff data, if those data are available. But if those data were not available, the IUH can be constructed from Synthetic Unit Hydrographs (SUH). In IUH the effective precipitation is applied to the drainage basin in zero time. Various methods were provided for determination of IUH, from which Clark`s SUH method is more applicable compared with the other methods. Clark`s method requires estimation of three basin parameters for the derivation of IUH, time of concentration (Tc), storage attenuation coefficient (K) and time-area histogram of the basin. In this study the required parameters for Clark`s SUH were derived using geographic information system (GIS), techniques. The results show good agreements between observed data hydrographs and Clark`s SUH which was derived by GIS techniques. This model was applied to the Kardeh river basin, in Khorasan province located in the northeast part of Iran. The results show that the Arcview GIS software is a powerful tool for IUH estimation.