Poly(2,2'-(1,4-phenylenedivinylene) bis-8-hydroxyquinaldine)/multi-walled carbon nanotube-modified glassy carbon electrode (poly(PBHQ)/MWCNTs/GCE) was developed and applied for the electrochemical estimation of vitamin B-12 (VB-12). Compared to multi-walled carbon nanotube-modified glassy carbon electrode, well-defined redox peaks were observed in phosphate buffer solution at pH 2.5. In contrast with the ill-defined redox peaks observed with unmodified glassy carbon electrode surfaces. The poly(2,2'-(1,4-phenylenedivinylene) bis-8-hydroxyquinaldine-based electrode displayed a good linear range of 0.1 to 10 mu M VB-12 with a low detection limit of 0.01 mu M. To further study the practical applicability of the proposed sensing procedure, the estimation of real samples was employed with satisfactory consequences. In addition, MWCNTs were used as sorbent for solid phase extraction (SPE) of vitamin B-12 from cereal food samples. Solid phase extraction parameters, such as the amount of MWCNTs, sample volume, pH, and type and amount of the eluent, were optimized.