β-Picolinium-p-chlorophenacylide (β-PCFY) acts as a retarder for polymerization of N-vinyl pyrrolidone. The polymerization runs were carried out at 60°C using benzene as an inert solvent. The kinetic equation for the present system may be written asRpα[β-PCPY]−1.0 [AIBN]0.66[N-VP]1.0. The value of overall energy of activation for polymerization in presence and absence ofβ-PCPY was computed as 44.0 and 42.3 kJ mol−1, respectively. The inverse relationship ofRp and¯Mv withβ-PCPY suggests thatβ-PCPY acts as a polymerization retarder. The retarding effect is also evidenced by higher initiator exponent value and higher value of energy of activation in presence of ylide. A mechanism is also proposed in which polymer propagating chain combines with one ylide component to give resonance stabilized radical.