New chiral N,C‐chelate organoboron compounds based on benzylideneamines (bza) with the general formula of B(bza‐R)Mes2 (R=H or Me; Mes=mesityl) are reported. A chiral substituent group R‐ or S‐CH(CH3)Ph (Ph=phenyl) was introduced to the imine center, which imposed a previously unobserved pseudo‐ or axial‐chirality on the BMes2, creating distinct diastereomers. NMR spectroscopic studies established that the diastereomers undergo slow exchange in solution at ambient temperature. The chiral N,C‐chelate B(bza‐R)Mes2 molecules undergo photoisomerization in the same manner as their non‐chiral analogues, generating chiral BN‐cyclooctatriene (BN‐COT) derivatives. Most significantly, by tracking the photoisomerization with circular dichroism (CD) and 1H NMR spectra along with time‐dependent density functional theory (TD‐DFT) computational studies, the photoisomerization was established to proceed in a highly stereoselective manner, that is, one diastereomer converts exclusively to the corresponding diastereomer product in the photoreaction.