Long-established corporations are generally considered stable. By examining the cases of the German pharmaceutical company Merck KGaA and US subsidiary Merck & Co., Inc. (MSD), this study examines the factors that influence corporate longevity. These two companies were once the same, with each originating from the Merck family drug store in Darmstadt, Germany, 350 years ago in 1668. Merck established its American branch in 1885. However, the two companies were separated during the First World WarWorld War in 1917 because MSD was expropriated at this time. Our hypothesis is that Merck achieved a more stable longevity than MSD on the basis of share price. However, the standard deviation of the share price of Merck ($28.27) is higher than that of MSD ($15.10) over a 20-year period, thus indicating that the share price of Merck significantly fluctuated; this contradicts our expectations for the longevity also stability of the long-established corporation. The main cause of this difference might be the capitalization of Merck of 30% of their capital as a limited partnership with shares in 1995. We hypothesize that a structural governance change occurred in both corporations owing to two aspects: on the one hand, emphasizing the legal status of the general partner in Merck’s family ownership structure and on the other, showing the heterogeneityheterogeneity of institutional investors in MSD’s ownership structure for MSD.