Boron-containing polymers have been demonstrated to be useful polymeric materials. However, the synthesis of boronic acid- or ester-containing polymers is highly challenging due to their instability and difficult characterization. This paper introduces N-methyliminodiacetic acid (MIDA) as a unique protecting group for the boronic acid to stabilize boron-containing polymers. The synthesized MIDA boronate stabilized polymers show remarkable stability to the air, moisture, and chromatography. Therefore, they could be used as a versatile platform for synthesizing other boronic acid- or ester-containing polymers. Postpolymerization modification also incorporates different functionalities by using this platform by Suzuki-Miyaura coupling. Both stability and versatility make MIDA boronate stabilized polymers have great potential applications in material and biomedical fields associated with borane chemistry.