Curative therapies with fewer adverse effects are required for cancer treatment. Medicinal plants represent a promising source of novel therapeutic candidates. We employed network pharmacology to predict potential molecular mechanisms of salvia root-derived tanshinone IIA (Tan IIA) in the treatment of colorectal cancer (CRC), followed by empirical validation. The Traditional Chinese Medicine System Pharmacology (TCMSP), DrugBank, and GeneCards databases were queried to identify overlapping Tan IIA (therapeutic)- and CRC (disease)-relevant protein targets. Cytoscape and STRING were used to generate component-target and protein-protein interaction (PPI) networks, respectively, and topology analysis identified highly connected nodes within the latter. Target proteins were subjected to gene ontology (GO)-based biological process annotation using DAVID, and to biological pathway enrichment analysis using the Kyoto encyclopedia and genome (KEGG) database. Enriched biological processes included cell cycling and proliferation, and enriched KEGG pathways included neuroactive ligand-receptor interaction, PI3K-Akt, and cancer. Network pharmacology results predicted that Tan IIA impacts multiple targets and pathways, but that its therapeutic effect is predominantly attributable to cell cycle regulation, inhibition of cell proliferation, and induction of apoptosis. Investigation of the in vitro impact of Tan IIA on proliferation, viability, and cell cycling of 2 hoursuman CRC cell lines (SW480 and SW620), using the CCK-8 method and flow cytometry, demonstrated that Tan IIA significantly inhibits cell proliferation via inducing cell cycle arrest in the G2/M phase. Network pharmacology-predicted hypotheses were thus empirically validated, providing a basis for in-depth study of the therapeutic mechanisms of Tan IIA in the context of CRC.