Self-assembly of miktoarm star-like AB(n) block copolymer in both selective solvent (A- or B-selective) and miscible homopolymer matrix (A or B homopolymer), that is, formation of micelles, was for the first time investigated by theoretical calculations based on self-consistent mean field theory. Interestingly, the calculation revealed that the size of micelles in solvent was smaller than that in homopolymer under the same conditions. In B-selective solvent, with increasing number of B blocks n in miktoarm star-like AB(n) block copolymer at a fixed volume fraction of A block, the micellar size decreased gradually. In stark contrast, when miktoarm star-like AB(n) block copolymer dissolved in B homopolymer matrix at molecular weight ratio of B homopolymer to AB(n) block copolymer f(H) = 0.30, the overall micellar size decreased nonmonotonically as the number of B blocks n in AB(n) block copolymer increased. The largest micelle was formed in AB(2) (i.e., n = 2). This intriguing finding can be attributed to a wet-to-dry brush transition that occurred from n = 1 to n = 2 in the micellization of miktoarm star-like AB(n) block copolymer. Moreover, the micellization behaviors of miktoarm star-like AB(n) block copolymer in A-selective solvent and A homopolymer matrix were also explored, where the overall micellar size in both scenarios was found to decrease monotonically as n in AB(n) block copolymer increased. These self-assembled nanostructures composed of miktoarm star-like AB(n) block copolymers may promise a wide range of applications in size-dependent drug delivery and bionanotechnology.