A sight glass retaining system is provided for mounting a sight glass to a support panel, such as for viewing combustion or other processes. The system includes a retainer which forms a continuous frame and has lateral flanges for locating the sight glass. Retaining tabs extend from the frame and support resilient retaining portions which snap into engagement with the support panel. A resilient element, which may form a seal with the sight glass and support panel, urges the assembly in compression to maintain tight engagement of the components, and generally column loads the retaining portions to preclude movement of the assembly on the support panel.