A method and system for measuring stray light for use in an exposure apparatus uses an image sensor to be disposed at a wafer level in the exposure apparatus. The stray light is measured by preparing a reference pattern and a measuring pattern on a reticle. The reference pattern includes a light shielding region having first open regions for transmitting light to a center of an active region of the image sensor. The measuring pattern includes a light shielding region having second open regions for transmitting light to a periphery of the active region. A first intensity of light reaching the active region after being filtered by the reference pattern and a second intensity of light reaching the image sensor after being filtered by the measuring pattern are measured. The intensity of the stray light is evaluated by a difference between the first and second light intensities.