Direct analysis in real-time ionization coupled with mass spectrometry (DART–MS) was first applied for the rapid determination of gamma-aminobutyric acid (GABA) in foods. Samples of germinated barley and fermented beans containing GABA at different levels were used, and the results were compared with those obtained by ultrahigh-performance liquid chromatography coupled with electrospray ionization triple quadrupole mass spectrometry (UHPLC–ESI–MS). After a series of optimization, a simple sample extraction procedure using 30% methanol aqueous solution was conducted, followed by direct determination of sample extracts without chromatographic separation or prior derivatization. The optimized DART–MS method exhibited low limits of detection (0.040 mg·kg−1) and good recovery rates (88.6%–104%). The Aspergillus oryzae-fermented black beans produced the highest amount GABA. The results for the samples slightly varied between DART–MS and UHPLC–ESI–MS. Current findings indicate that DART–MS could be a high-throughput alternative to classic UHPLC–ESI–MS.