On the basis of a method of estimating the diurnal amplitude of sea surface temperature (SST) as a function of the diurnal integrals of surface heat and momentum fluxes, a parameterization scheme of the diurnal cycle of SST is implemented in a one-dimensional ocean mixed-layer model. Many coupled ocean-atmosphere models using bulk mixed-layer schemes underestimate the diurnal cycle in sea surface temperature by up to 2¿C. This discrepancy is caused by coarse vertical resolution in the upper grid boxes of the ocean components. A simple solution is suggested by adding one extra transient level: a variable-depth diurnal sublayer within the top model level which accommodates the diurnal buoyancy cycle. A one-dimensional mixed-layer model with 10-m resolution and with sublayer simulates diurnal SSTs close to those observed from the Tropical Ocean Global Atmosphere/Coupled Ocean Atmosphere Response Experiment (TOGA/COARE) with typical errors of about 0.1¿C. The impact of improved SSTs on surface heat fluxes is also shown by coupling the one-dimensional mixed-layer model with sublayer to an atmospheric boundary layer model.