A highly sensitive, rapid assay method has been developed and validated for the estimation of nobiletin in rat plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive-ion mode. The assay procedure involves extraction of nobiletin and citalopram (internal standard, IS) from rat plasma with liquid-liquid extraction. Chromatographic separation was achieved using an isocratic mobile phase (0.2% formic acid-acetonitrile, 20:80, v/v) at a flow rate of 0.6 mL/min on an Atlantis dC₁₈ column (maintained at 40 ± 1 °C) with a total run time of 2.0 min. The MS/MS ion transitions monitored were 403.2 → 373.0 for nobiletin and 325.2 → 109.0 for IS. Method validation was performed as per Food and Drug Administration guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.05 ng/mL and the linearity range extended from 0.05 to 51.98 ng/mL. The intra- and inter-day precisions were in the range of 1.96-14.3 and 6.21-12.1, respectively.