The Drosophila olfactory system is highly stereotyped in both form and function. Not only are olfactory receptor neurons (ORNs) expressing specific odorant receptors (ORs) found in the same part of the antenna in every fly, but the axons of all the ORNs that express the same OR converge on the same glomerulus in the antennal lobe. This stereotypy and precise connectivity of the fly olfactory system raises significant questions about its origin and the mechanisms that regulate OR expression. Although several transcription factors have been already implicated in a combinatorial code that specifies OR expression and thus ORN identity, it is clear several players remain unidentified. We therefore designed a microRNA (miRNA)-based over-expression screen to identify and validate previously unknown transcription factors that regulate OR expression. After identifying a group of miRNAs whose over-expression disrupts OR expression, we performed a secondary gene-specific RNAi screen of their predicted targets to identify novel regulators of Or47b expression. This allowed us to identify the transcription factor Atf3 as a regulator of OR expression. In subsequent analysis, we also found the known Atf3 binding partner Jun, itself a bZIP transcription factor, and the related transcription factor Fos also play roles in regulating OR expression.