Multiferroic YMn₂O₅ fine powders were synthesized by a hydrothermal process from Y(NO₃)₃ · 6H₂O and Mn(NO₃)₂, and their structure and magnetic characteristics were evaluated. YMn₂O₅ fine powders with orthorhombic structure were synthesized by the present process with aqueous NaOH as the mineralizer, and the synthesis conditions such as temperature and [NaOH] have significant effects upon the grain size and morphology. The single phase YMn₂O₅ fine powders with the most uniform morphology were synthesized at 523 K from the solution with [NaOH] = 1 M, and then the good sinterability was expected at lower temperatures where the phase separation in YMn₂O₅ ceramics could be avoided. YMn₂O₅ fine powders derived by the present hydrothermal process indicated the weak ferromagnetism below 45 K.