Si/Al composite hollow spheres with a surface hole were prepared with the co-axial microchannel in a one-step method. It is easy to use the technique for size control and continuous operation. At Si/Al ratio between 4 and 5, a hole forms on the surface, due to the fast gelation process and high viscosity of the sol. Scanning electron microscopy, nitrogen adsorption-desorption isotherms, and mercury intrusion method are used to characterize the samples. The hole size is 40-150 mu m and the particle size is 450-600 mu m. The size can be adjusted by the flow rate of the oil phase. (C) 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.