Abstract: With the development of offshore engineering, increasing attention has been devoted to the safety of the underwater structures, such as the bottom-supported piles of offshore oil drilling platforms and offshore petroleum pipelines. For internal solitary waves (ISWs) exert a neglected influence on the safety of underwater structures, studying ISW forces acting on cylinders is highly significant. Only a few studies have been conducted on ISW forces acting on cylinders, and studies that compare the forces acting on circular and square cylinders in a stratified fluid environment are scarce. Experimental investigations of the forces exerted by ISWs on circular and square cylinders are performed in a stratified fluid tank using a new device to generate ISWs and a measurement system for ISWs loads. Comparisons of ISW force behaviors in the two cylinders are studied at various ISW amplitudes. Results show that the forces exerted on the circular and square cylinders increase with increasing wave amplitudes. At the same wave amplitude, the ISW forces on the square cylinder are larger than those on the circular cylinder. This study provides guidance for cylinder design and safety evaluation in a stratified fluid environment.