The effects of the molecular structure of phenolic resins on the Mark–Houwink–Sakurada (MHS) equation and the conformation in acetone solution were studied. The exponent in the MHS equation was remarkably less than that for linear polymers such as vinyl polymers, cellulose derivatives, and so on. As the cause, the branching and the hydrogen bonding between hydroxyl groups of the neighboring phenolic nuclei were considered. Several kinds of phenol-p-cresol and phenol-p-tert-butylphenol cocondensation resins whose composition differs from one another were synthesized. Despite the difference in the degree of branching, the exponent in the MHS equation for each was approximately equal. On the other hand, the exponent for o-cresol novolak, which was rich in ortho-para methylene linkages was larger than the all-ortho novolak and p-cresol novolak, which were rich in ortho–ortho methylene linkages. Methylation of the phenolic hydroxyl group increased the value of the exponent. From these results, it became obvious that while the hydrogen bonding lowered the exponent in the MHS equation due to molecular conformation compaction in acetone solution, the molecular branching had little effect on the exponent α.