The chain-length dependence of the termination rate coefficient, kt, of bulk homopolymerizations of n-butyl methacrylate (n-BMA) and tert-butyl methacrylate (t-BMA) at ambient pressure and temperatures between -30 and 60 °C has been studied via the single pulse-pulsed laser polymerization-electron spin resonance (SP-PLP-ESR) technique. The decay of radical concentration, cR, after laser SP initiation is monitored with a high time resolution of microseconds by ESR spectroscopy. Radical chain length, i, increases linearly with time t after applying the laser pulse. The experimental kti,i values refer to rate coefficients for termination of two radicals of identical chain length i. The variation of kti,i with chain length is adequately represented via the composite model proposed by Smith et al., in which two power-law expressions, kti,i ∝ i-α, are contained with the exponents αs and αl referring to short-chain and long-chain radicals, respectively. The transition between the two regimes occurs at the crossover chain length, ic. The rate coefficients extrapolated for termination of two radicals of chain length unity, kt1,1, are almost identical for n-BMA and t-BMA with an activation energy of EA(kt1,1) ≈ 10 kJ mol-1. The αs values are close to each other: 0.65 ± 0.10 (n-BMA) and 0.56 ± 0.10 (t-BMA). Both αl values are found to be 0.20 ± 0.05, which is close to the theoretical value of αl = 0.16. The crossover chain lengths are ic ≈ 50 for n-BMA and ic ≈ 70 for t-BMA. The minor differences in composite-model parameter values of n-BMA and t-BMA are assigned to differences in chain mobility.