The invention provides a method for preparing a nano zinc oxide employing a catharanthus roseus leaf extract. The method comprises the following steps: A pretreatment of blades; B preparation of blade extracts; C preparation of the nano zinc oxide; and D burning. The nano zinc oxide is prepared without a template through a biological method, so that the method is simple, feasible, low in cost, environmental friendly, and has potential important application in the fields such as photocatalysis, ceramics, gas sensors and power cells.