A thin film deposition apparatus can be simply applied to produce large-sized display devices on a mass scale and improves manufacturing yield. The thin film deposition apparatus for forming a thin film on a substrate includes: a deposition source that discharges a deposition material; a deposition source nozzle unit disposed at a side of the deposition source and including a plurality of deposition source nozzles arranged in a first direction; and a patterning slit sheet disposed opposite to the deposition source nozzle unit and including a plurality of patterning slits arranged in the first direction; wherein each of the patterning slits includes a plurality of sub-slits.