Abstract: Slotted breakwaters have been used to provide economicalprotection from waves in harbors where surface waves and currents may co-exist. Inthis paper, the effects of currents on the wave scattering by slotted breakwatersare investigated by using a simple model. The model is based on a long waveapproximation. The effects of wave height, barrier geometry and current strength onthe reflection and transmission coefficients are examined by the model. The modelresults are compared with recent experimental data. It is found that boththe wave-following and wave-opposing currents can increase the reflectioncoefficientand reduce the transmission coefficient. The model can be used to study theinteraction between long waves and slotted breakwaters in coastal waters.