Fatty acids have multitudinous biological functions and play a crucial role in many biological processes, but due to poor ionization efficiency and lack of appropriate internal standards, the comprehensive quantification of fatty acids by liquid chromatography-tandem mass spectrometry is still challenging. In this study, a new, accurate, and reliable method for quantifying 30 fatty acids in serum using dual derivatization was proposed. Indole-3-acetic acid hydrazide derivants of fatty acids were used as the internal standard and indole-3-carboxylic acid hydrazide derivants of them were used to quantify. The derivatization conditions were systematically optimized and the method validation results showed good linearity with R2  > 0.9942, low detection limit (0.03-0.6 nM), precision (1.6%-9.8% for intra-day and 4.6%-14.1% for inter-day), recovery (88.2%-107.2% with relative standard deviation < 10.5%), matrix effect (88.3%-105.2% with the relative standard deviation < 9.9%) and stability (3.4%-13.8% for fatty acids derivants in 24 h at 4°C and 4.2%-13.8% for three freeze-thaw cycles). Finally, this method was successfully applied to quantify fatty acids in serum samples of Alzheimer's patients. In contrast to the healthy control group, nine fatty acids showed a significant increase in the Alzheimer's disease group.