Boron isotope values in Paleozoic brachiopods and corals, collected from the Yunnan-Guizhou Plateau, China, can be used to constrain the boron isotope compositions of past oceans. All brachiopod shells and coral samples were screened for diagenetic recrystallization by cathodoluminescence microscopy, trace element geochemistry of B, Fe, Mn, Sr, and scanning electron microscopy. The boron isotope ratios for brachiopods in Silurian, Devonian, Carboniferous, and Triassic calcites are in the ranges 8.9aEuro degrees aEuro"14.0aEuro degrees, 8.8aEuro degrees aEuro"13.8aEuro degrees, 10.3aEuro degrees aEuro"16.3aEuro degrees, and 6.7aEuro degrees aEuro"12.4aEuro degrees, respectively. The boron isotope ratios of coral calcites in the Silurian, Devonian, and Permian are 9.1aEuro degrees aEuro"12.2aEuro degrees, 6.1%-13.8aEuro degrees, and 9.2aEuro degrees aEuro"16.1aEuro degrees, respectively. The delta (11)B values for both brachiopods and corals are significantly lower than those for modern biogenic carbonates, indicating that the Paleozoic oceans were depleted of delta (11)B by up to 10aEuro degrees. Our results are consistent with previous published studies. The boron isotope compositions of corals and brachiopods show the consistent trends. The low delta (11)B values may be explained by an enhanced riverine flux of boron from the continents.