In order to improve the potential of celastrol against non-small-cell lung cancer cells, the privileged structure, thiazolidinedione, was introduced into its C-20 carboxylic group with acetylpiperazine as a linker, and the thiazolidinedione-conjugated compounds 10a-10t were prepared. The target compounds were evaluated for their cytotoxic activities against the A549 cell line, and the results showed that most of the compounds 10a-10t displayed improved potency over celastrol, and compound 10b exhibited significant activity against the A549 cell line, with an IC50 value of 0.08 μM, which was 13.8-fold more potent than celastrol (IC50 = 1.10 μM). The mechanistic studies suggested that 10b could induce A549 cell apoptosis, as evidenced by Hoechst 33342 staining and annexin V-FITC/propidium iodide dual staining assays. Western blot analysis suggested that compound 10b could upregulate Bax expression, downregulate Bcl-2 expression, and activate the mitochondria-mediated apoptotic pathway. Furthermore, compound 10b could effectively inhibit tumor growth when tested in an A549 cell xenograft mouse model. Collectively, compound 10b is worthy of further investigation to support the discovery of effective agents against non-small-cell lung cancer.