The research for innovative treatments against colon adenocarcinomas is still a great challenge. Acacia catechu Willd. heartwood extract (AC) has health-promoting qualities, especially at the gastrointestinal level. This study characterized AC for its catechins content and investigated the apoptosis-enhancing effect in human colorectal adenocarcinoma HT-29 cells, along with its ability to spare healthy tissue. MTT assay was used to describe the time course, concentration dependence and reversibility of AC-mediated cytotoxicity. Cell cycle analysis and AV-PI and DAPI-staining were performed to evaluate apoptosis, together with ROS formation, mitochondrial membrane potential (MMP) changes and caspase activities. Rat ileum and colon rings were tested for their viability and functionality to explore AC effects on healthy tissue. Quantitative analysis highlighted that AC was rich in (±)-catechin (31.5 ± 0.82 mg/g) and (−)-epicatechin (12.5 ± 0.42 mg/g). AC irreversibly decreased cell viability in a concentration-dependent, but not time-dependent fashion. Cytotoxicity was accompanied by increases in apoptotic cells and ROS, a reduction in MMP and increases in caspase-9 and 3 activities. AC did not affect rat ileum and colon rings' viability and functionality, suggesting a safe profile toward healthy tissue. The present findings outline the potential of AC for colon cancer treatment.3 of 17 at approximately the same content level was observed (Figure 1b). The latter was assumed as a marker of the epimerization as the consequence of the process applied in decoction preparation (thermal treatment). Analysis of decoction preparations stored during very long-term period (at least two years) at room temperature in the dark, did not show loss of (−)-EC and (+)-C, nor epimerization progression, thus suggesting very high chemical stability of the preparation. Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 3 of 17 period (at least two years) at room temperature in the dark, did not show loss of (−)-EC and (+)-C, nor epimerization progression, thus suggesting very high chemical stability of the preparation.