Drug target identification is a critical step towards the understanding of the mechanism of action of a drug, which will help to improve the current therapeutic regime and to expand the drug’s therapeutic potential. However, current in vitro affinity chromatography-based and in vivo activity- based protein profiling (ABPP) approaches generally face difficulties discriminating specific drug targets from non-specific ones. Here we describe a novel approach combining isobaric tag for relative and absolute quantitation (iTRAQ) with Clickable ABPP, named ICABPP, to specifically and comprehensively identify the protein targets of andrographolide (Andro), a natural product with known anti-inflammation and anti-cancer effects, in live cancer cells. We identified a spectrum of specific targets of Andro, which furthered our understanding of the mechanism of action of the drug. We found that Andro has a potential novel application as the tumor metastasis inhibitor, which was validated through cell migration and invasion assays. Moreover, we have unveiled the target binding mechanism of Andro with a combination of drug analogue synthesis, protein engineering and mass spectrometry-based approaches and determined the drug-binding sites of two protein targets, NF-kappaB and actin.