The present invention provides a method for manufacturing zinc oxide whiskers, whereby zinc powders composed of particles coated with an oxide film, preferably an oxide film having a superior sealing property are, heated for oxidization in an atmosphere containing oxygen.The atmosphere may contain carbon dioxide or steam.The obtained zinc oxide whiskers are formed in a single crystal comprised of a core part and an acicular part spreading in four different directions from the core part.For a baking furnace to obtain zinc oxide whiskers, is employed one that successively forms an atmosphere of a high partial pressure of zinc steam at the source side and an atmosphere of a high partial pressure of oxygen for facilitating formation of whiskers. The zinc oxide whiskers can be controlled in size by selecting the relative ratio of the partial pressure of zinc steam and oxygen.Accordingly, zinc oxide whiskers obtained by the present invention are formed in a single crystal without anisotropy, thereby being applicable to a variety of constructional or electronic materials with no anisotropy in strength and electric properties. Because the resultant crystal is several hundreds .mu.m, the zinc oxide whiskers may be mixed with metals, ceramics or synthetic resins, etc. to increase the mechanical strength thereof remarkably.