A measuring head for determining particle size in transparent media, comprising a measuring head body which has an opening for an optical measuring point with two measuring windows, consisting of an illuminating device and a light receiving device which is connected to an opto-electronic converter device. A rinsing device is used to clean the optical measuring point. The windows can be reliably prevented from becoming fouled or wetted by particles contained in the particle flow, enabling optical permeability of the measuring point and avoiding false measuring values. The rinsing device has a rinsing medium source, a channel extending to the opening inside the measuring head body for delivery of a rinsing medium and at least one discharge opening near the opening, which extends perpendicularly to and directly in front of the measuring windows. At least one defined rinsing jet is spread over the surfaces of the measuring windows.
