A modified high‐pressure, stopped‐flow apparatus has been developed to enable kinetic experiments to be monitored spectrophotometrically to 200 MPa, with efficient mixing of the reactant solutions. This apparatus is compact, relatively inexpensive to construct, and the solutions are only exposed to inert materials, such as Kel‐F, Teflon, quartz (low‐pressure windows), and glass or Viton. The drive‐syringe pistons are propelled by a step motor housed on top of the stopped‐flow unit inside the pressure vessel, resulting in a dead time for the system of ∼10 ms at 25 °C.