A direct numerical simulation (DNS) based on a finite volume method is applied to a particle-laden turbulent mixing layer in order to examine effects of loaded particles on turbulence and scalar diffusion. Trajectories of all particles are individually pursued with a Lagrangian method. The results show that the small particles, whose response time, τp, is smaller than the Kolmogorov time scale, τ k, reduce the turbulent intensities of streamvrise and transverse velocity fluctuations upstream of the mixing layer. However, the streamwise slope of turbulent intensities becomes high as compared to particle-free flow downstream of the mixing layer. Because source terms, which are energy exchange and turbulent production terms for the turbulent intensity of streamwise velocity fluctuation and pressure strain correlation term for that of transverse velocity fluctuation, are increased. Furthermore, the small particles increase the mean squared values of the concentration fluctuations.