The termination kinetics of dibutyl itaconate (DBI) bulk polymerization was studied via SP-PLP-ESR single pulse-pulsed laser polymerization with time-resolved detection of free-radical concentration by electron-spin resonance, at temperatures between 0 and 60 °C. As is characteristic of PLP experiments, termination rate coefficients, kt(i,i), are measured for radicals of (almost) identical chain length (CL) i. CL-averaged ⟨kt⟩, for chain lengths up to 200 monomer units, and also kt0 referring to termination of very small-size radicals are directly deduced from measured DBI radical concentration vs time traces. At 45 °C, ⟨kt⟩ is (3.4 ± 0.6) · 105 L · mol-1 · s-1 and kt0 is (7.2 ± 1.0) · 105 L · mol-1 · s-1. Both rate coefficients are independent of monomer conversion up to the highest experimental conversion of 18%. The associated activation energies are EA(⟨kt⟩) = 23.0 ± 3.2 kJ · mol-1 and EA(kt0) = 27.6 ± 2.8 kJ · mol-1, respectively. “Model-dependent” and “model-free” analyses of radical concentration vs time profiles indicate a pronounced CL dependence of kt(i,i) for DBI radicals of moderate size, 5 < i < 50. The lowering of kt(i,i) with CL corresponds to an exponent α close to 0.5 in a power-law expression kt(i,i) = kt0 · i-a. At higher chain lengths, the variation of kt(i,i) with CL becomes weaker and may be represented by an α value of 0.16 or even below. These results are consistent with models according to which α varies to a larger extent at low CL and to a smaller extent at high CL with the crossover region between the two ranges being located somewhere around i = 100.