The Ethiopian Ashange formation is an extensive development of fissural and central typerneruptions in Oligocene period (~ 30 mas) that produced a thick succession of the trap seriousrnbasalts that forms mainly the north western and southern Ethiopian plateau (see Fig.3). ThernAshange basalt is thus considered to be the lower formation in the stratigraphy of Ethiopianrnvolcanic plateau commonly injected by dolerite sills, acidic dykes and other intrusions. Itrncovers an area and volume of about 85,000km2 and 66,300 m3 respectively contributing to 37 %rnof the overall volume of Ethiopian continental flood basalts. A total of 70 wells raw pumping test data are analyzed and used besides their respective lithological log to determine hydraulic property of Ashange formation. The dominant aquifer types recognized after analysis are consolidated, confined, double porosity and single plane vertical fractured aquifer systems. Ashange formation shows decreasing aquifer productivity with respect to increased drilled boreholes depth and age of formation. The established relationship between T and Sp.Ca data also shows R2 value 0.957 that shows Sp.Ca can be used as fair estimator of T in areas with only Sp.Ca data.rnA relatively less well loss coefficient is observed in the Ashange formation where the existingrnvariation still indicates the existence of improper well site location, improper well design andrnconstruction factors and well yield deteriorations with time due to clogging, corrosion andrnincrustation activities of well screens. Comparison of transmissivity values of the EthiopianrnAshange formation with other continental flood basalts of the world shows a decreasing trendrnwith respect to age which may be related to the gradual closing up of open spaces like fracturesrnby secondary materials hindering free flow as well as storage of water .The productivity ofrnAshange formation can be generally categorized as moderate to high which is controlled byrnlocation and geomorphologic setup of the formation outcrop; hydrothermal processes and nature;rnextent, frequency and orientation of the associated structural features and nature and degree ofrnweathering. This work can be considered as an effort to characterize the whole aquifer system ofrnEthiopia for a better understanding of the available ground water reserve and distribution forrnfurther use in developmental activities.rnrnKey words:-Ashange,;Flood basalts,; Aquifer;, Pumping test;Theoretical relations, Transmissivity; Specific capacity