The mean-square optical anisotropy [Gamma(2)] was determined from anisotropic light-scattering measurements for 10 samples of isotactic oligo- and poly(methyl methacrylate)s (i-PMMA), each with the fraction of racemic diads f(r) similar or equal to 0.01, in the range of weight-average molecular weight from 3.58 x 10(2) (trimer) to 1.07 x 10(4), and also for methyl isobutyrate (the monomer of PMMA), in acetonitrile at 28.0 degrees C (Theta). A comparison is made-of the present data with the helical wormlike (HW) chain theory with the values of the model parameters previously determined from the mean-square radius of gyration [S-2] and with the local polarizability tenser properly assigned to the repeat unit of the chain in the same manner as in the previous study of atactic (a-) PMMA, i.e., evaluated with the same bond polarizabilities. It is shown that the HW theoretical values may reproduce quantitatively the experimental results in the range of weight-average degree of polymerization x(w) greater than or equal to 6. The disagreement between theory and experiment for x(w) less than or equal to 5 may probably be due to effects of chain ends. A Comparison is also made of the present results with the previous ones for a-PMMA, leading to the conclusion that the HW theory may explain the f(r) dependence of [Gamma(2)] as well as of [S-2], the scattering function, and steady-state transport coefficients.