Dynamic light scattering measurements have been made on 14 samples of a polymacromonomer consisting of polystyrene with 15 styrene side-chain units in cyclohexane at 34.5 degrees C (the theta point) to determine the translational diffusion coefficient D as a function of molecular weight. The dependence of D on the main-chain length is analyzed on the basis of the wormlike chain by taking into account the end effect arising from side chains near the main-chain ends. The model parameters describing this dependence, i.e., the Kuhn segment length (11.5 +/- 1.5 nm), the linear mass density (5600 +/- 700 nm(-1)), the diameter (5.2 +/- 0.5 nm), and the end-effect parameter delta (2.5 +/- 0.3 nm), are close to those determined previously from (z) z-average mean-square radius of gyration) and [eta] (the intrinsic viscosity), leading to the conclusion that the wormlike chain model is capable of consistently explaining (z) [eta], and D of the polymacromonomer in the Theta solvent.