The oxidation of light alkanes, particularly ethane, was examined over Cs-M/SiO2 catalysts (M = Fe, V, Bi). Turn-over-frequency (TOF) and product selectivities were strongly dependent on the loading amounts of M. When the loading amounts of M were less than 0.1 at.% to Si, very high TOF and relatively high selectivities to acetaldehyde and acrolein were observed. The isolated site or mononuclear structure of Fe, V or Bi on the Cs/silica surface is vital for the high aldehyde yields. Cesium was also important for the high reactivity of ethane and the high aldehyde selectivities. The reaction pathways giving acrolein from ethane and the roles of catalytic components are discussed.