Non-steroidal anti-inflammatory drugs (NSAIDs) are a class of drugs that are mainly used to treat pain, inflammation, and fever via cyclooxygenase-2 (COX-2) inhibition. There are abundant findings that uncover the hidden critical chemotherapeutics potential of NSAIDs in cancer treatment. However, still the precise mechanism by which NSAIDs could be used as an effective anti-tumor agent in the prevention of carcinogenesis is not well understood. Here, we show that indomethacin, a well-known NSAID, induces proteasomal dysfunction that results in accumulation of unwanted proteins, mitochondrial abnormalities, and successively stimulate apoptosis in cells. We observed the interaction of indomethacin with proteasome and noticed the massive accumulation of intracellular ubiquitin-positive proteins, which might be due to the suppression of proteasome activities. Furthermore, we also found that exposure of indomethacin causes the accumulation of critical proteasomal substrates that consequently generate severe mitochondrial abnormalities and prompt up key apoptotic events in cells. Our results demonstrate how indomethacin affects normal proteasomal functions and induces mitochondrial apoptosis in cells. These findings also improve our current understanding of how NSAIDs can exhibit crucial anti-proliferative effects in cells. In near future, our findings may suggest a new possible strategy for the development of specific proteasome inhibitors in conjunction with other chemo-preventive anticancer agents. © 2017 Wiley Periodicals, Inc.