In Chilean traditional medicine, Aristotelia chilensis (Mol) Stuntz is commonly utilized for a variety of conditions (particularly digestive problems). We investigated the effects of an aqueous extract from the fruit pulp of A. chilensis (Maqui berry: M2) on endoplasmic reticulum stress and mitochondrial pathway-induced early apoptosis in Ishikawa cells. Using the MTT assay, the aqueous extract was found to have an inhibitory impact on human endometrial cancer Ishikawa cells, with an IC50 of 5.36 μg/mL. The changes in Ishikawa cells under the effect of M2 were detected by flow cytometry with cycle arrest in S phase, reduced mitochondrial membrane potential, ROS and calcium ion aggregation. Western blotting and RT-qPCR were used to identify the intracellular mRNA and protein alterations. The presence of M2 resulted in the up-regulation of mitochondrial pathway-related proteins Bad, Bax, and Cyto C, down-regulation of Bcl-2, and up-regulation of endoplasmic reticulum stress-related proteins IRE1α, p-eif2α, ATF4, and CHOP. The findings imply that A. chilensis pulp may be used as a possible raw material for the innovative functional applications.