The invention discloses mono-disperse gallium oxide powder and a method for preparing high-density ceramic targets from the mono-disperse gallium oxide powder. The method includes dissolving metal gallium materials with the purity higher than 99.99% in acid and preparing clear gallium salt solution; adding precipitants into the clear gallium salt solution to generate precipitates; washing, filtering, drying and calcining the obtained precipitates to obtain the mono-disperse ultrafine gallium oxide powder; carrying out compression molding and cold isostatic pressing strengthening on the synthesized mono-disperse gallium oxide powder to obtain gallium oxide green bodies; sintering the green bodies in high-temperature furnaces to obtain the high-density gallium oxide ceramic targets with uniform microscopic structures. The mono-disperse gallium oxide powder and the method have the advantages of simple process, convenience in operation, high yield, applicability to industrial production and the like.