Solid state NMR studies revealed the hydrogen bonding network characteristics and the substantial changes of molecular motion in phenolic/PEO blend. The PEO crystallinity was reduced owing to the formation of strong hydrogen bonding between PEO and phenolic, as revealed by 13C chemical shift and DSC. Both T1ρ H relaxation behavior at high field and T1 H relaxation time distribution taken at low field reflected the substantial increase of molecular segmental mobility upon blending. The maximum flexibility appeared at 40/60 (phenolic/PEO) composition is attributed to the balance between the amount of amorphous PEO and the effective pairing of hydrogen bonding between the two components. The seemingly contradicting results between the increase of overall motion with the free volume contraction and glass temperature elevation has raised the point that these measurements are ensemble averages of different length scales. Correlation between properties and motion revealed by spin relaxation should proceed with caution.