A rapid, sensitive, and specific high-performance thin-layer chromatographic (HPTLC) method was developed and validated for quantitative determination of free duloxetine (DLX) in human serum. Densitometric analysis of free DLX was carried out at 235 nm after simple liquid-liquid extraction. The method uses thinlayer chromatography (TLC) aluminum plates pre-coated with silica gel G 60 F254 as stationary phase and acetone-benzene-triethylamine (5:4.5:0.5, v/v) as mobile phase for the separation of free DLX from serum constituencies. The calibration curve was linear (r2 = 0.980) in the tested range of 35–140 ng spot−1 with a limit of quantification and detection of 35 and 10 ng spot−1 with the recovery of free DLX in serum ranges from 92.86 to 97.58%. Intra- and inter-day precision (% RSD) values were ≤1.83% and ≤5.66%, respectively. Analysis of free DLX from human serum was successfully performed without interference from endogenous materials and some of the other common drugs of abuse. The method’s ability to quantify free DLX with precision, accuracy, and sensitivity makes it useful in forensic examination.