Excessive endoplasmic reticulum stress (ERS) disrupts protein translation, protein folding, and calcium homeostasis and may contribute to ischemia-reperfusion injury. Saponins extracted from the stems and leaves of Panax quinquefolium (PQS) protect rat myocardium against ischemia-reperfusion injury, but it is not known if suppression of ERS contributes to cardioprotection. Neonatal rat cardiomyocytes were subjected to hypoxia-reoxygenation (H-R) in the presence of PQS or vehicle. Cell injury and apoptosis were assayed by trypan blue exclusion, lactate dehydrogenase activity, and flow cytometry. In addition, reverse transcriptase-polymerase chain reaction and Western blotting were used to examine mRNA and protein expression of the ERS-related proteins glucose-regulated protein 78, calreticulin, CCAAT/enhancer-binding protein homologous protein, and caspase-12, as well as the apoptosis-associated proteins Bax and Bcl-2. We confirmed that PQS protects cardiomyocytes from H-R-induced injury and apoptotic cell death. Furthermore, PQS suppressed H-R-induced excessive ERS, as evidenced by reduced caspase 12 activation and decreased glucose-regulated protein 78, calreticulin, and CCAAT/enhancer-binding protein homologous protein overexpression. These results indicated that PQS could alleviate H-R injury of cardiomyocytes, which would be probably related to inhibiting excessive ERS induced by H-R.