Bénard-Marangoni convections of two-layer fluids heated from the bottom are investigated experimentally with a particle imagine velocimetry.The flows are visualized from the side,and various velocity fields near the onset of convection,such as three-layer vortex convective pattes,are observed when the depth ratio varies in a wide range.A new classification of the convective pattes is proposed with more detail than in previous studies.The analysis of the results indicates that the interface tension greatly influences the motion intensities of the bottom and top layers.The dimensionless wave number increases with the Bond number when the motion in the top layer is not more intense than that in the bottom layer,which agrees with the theoretical prediction.