For the experiment of the friction drag reduction by microbubble injection, a drag reduction water tunnel was specifically designed and made. Experimental apparatus and procedures were devised and developed for measuring the change of wall friction drag with microbubble injection. For fully-developed channel flows. the change of friction drag with important parameters of microbubble injection is investigated and the experimental data and results obtained are presented. The amount of friction drag reduction up to 25% is observed in the present study.