The isothermal crystallization kinetics of a series of poly(alpha-olefin) bottlebrushes, with side-chain lengths (N-sc) ranging from 10 to 16 carbons, was systematically investigated via differential scanning calorimetry (DSC), small- and wide-angle X-ray scattering (SAXS/WAXS), small-angle light scattering (SALS), and polarized optical microscopy (POM). Analysis of the DSC data with the Avrami model reveals that crystallization proceeds via one-dimensional growth of rod-shaped crystallites (fibrils), which is unprecedented in semicrystalline polymers. Both the nucleation and crystallization rates, as well as the equilibrium melting temperature (obtained by the linear Hoffman-Weeks extrapolation method), are increasing functions of N-SC, which results from the decreasing energy barrier for crystallization as the side chains are longer. Analysis of the crystallization kinetics with the Lauritzen-Hoffman theory revealed two stages of crystallization. The transition from regime I to regime II occurs at undercooling values that decrease with N-SC and range from 10 K, for poly(1-octadecene), to 45 K, for poly(1-dodecene). Analysis of the crystal structure (via SAXS/WAXS, SALS, and POM) during isothermal crystallization showed an increase in crystallinity and a decrease in interfibril distance as undercooling deepens, as well as the development of bicontinuous crystal domains.