A positioning device for shelves includes a support and a sleeve, the support has a first end and a second end. A tail board extends from the first end and a notch is defined in the tail board. The sleeve has a passage defined axially therethrough and at least one stop extends inward from the inner periphery of the passage. The tail board is inserted into the passage and the stop is engaged with the notch so as to secure the support to the passage. An engaging portion is located in the notch and located corresponding to the stop.