An easy, safe and low-cost synthesis of conjugated microporous polymers and related carbonized microporous materials is highly desirable for practical use. Here, we report the synthesis of 9,9′-spirobifluorene-based conjugated microporous organic polymers (COPs) starting from unsubstituted spirobifluorene using an inexpensive FeCl₃ mediator. Three kinds of COPs, synthesized by FeCl₃-mediated oxidative polymerization, Friedel–Crafts polymerization, and competitive oxidative/Friedel–Crafts polymerization of the spirobifluorene precursor, showed large surface areas (940–1980 m² g⁻¹) and high micropore volumes (0.5–0.9 cm³ g⁻¹). The COPs synthesized by competitive oxidative/Friedel–Crafts polymerization were found to show a high gas uptake ability which is almost comparable to that of the previously reported spirobifluorene-based microporous organic polymers prepared by Yamamoto polymerization using an expensive Ni catalyst. The COPs were easily transformed into microporous carbons by direct carbonization without the addition of any activating agents. The carbonization process enhanced the gas uptake ability of the COPs at low pressure (1 atm), although the surface area and micropore volume were almost unchanged or slightly decreased. The FeCl₃-mediated competitive oxidative/Friedel–Crafts polymerization of non-functionalized aromatics would be a useful synthetic approach for an easy, safe and low-cost synthesis of conjugated microporous polymers.