Turbulent shear flows over a concave surface are subjected to streamline curvature. The objective of the present paper is to clarify experimentally the turbulence kinetic energy and shear stress balance in a boundary layer having a mild surface curvature without substantial pressure gradient. Each term in the transport equation for the turbulence kinetic energy and shear stress is deduced from the data. The extra rate of mean strain 2kU due to curvature makes a positive contribution to the production of v^-2. The effect of the concave curvature on the production of the Reynolds stress - (uv)^^^ is larger than the production of the turbulence kinetic energy. The structure of the turbulent boundary layer over a concave surface is prescribed by the energy balance.