Using the constant addition technique, the coprecipitation of lanthanum, gadolinium, and lutetium with aragonite in seawater was experimentally investigated at 25 ℃. Their concentrations in aragonite overgrowths were determined by inductive coupled plasma mass spectrometer. All these lanthanides were strongly enriched in aragonite overgrowths. The amount of lanthanum, gadolinium, and lutetium incorporated into aragonite accounted for 57%-99%, 50%-89%, and 40%-91% of their initial total amount, respectively. With the increase of aragonite precipitation rate, more lanthanides were incorporated into aragonite while their relative fraction in aragonite overgrowths decreased consistently. It indicated that the coprecipitation of lanthanides with atagonite was controlled by the kinetics of aragonite precipitation.