Polymer microsphere composed of monodispersed poly(4-vinyl pyridine) core-polystyrene (PS) shell [poly(4-vinyl pyridine) 28 mol %; number-average molecular weight (M(n)BAR) of shell chain, 8.0 x 10(4); arm number, 1400] was blended with poly(styrene-b-2-vinyl pyridine) diblock copolymer [poly(2-vinyl pyridine) 30 mol%; M(n)BAR of PS = 2.0 x 10(4)], poly(styrene-b-isoprene) diblock copolymer (polyisoprene 28 mol%; M(n)BAR of PS = 2.6 x 10(4)) or poly(styrene-b-4-vinyl pyridine) diblock copolymer [poly(4-vinyl pyridine) 17 mol%; M(n)BAR of PS = 3.9 x 10(5)]. The morphology of the blend was investigated by transmission electron microscopy. When M(n)BAR of the diblock copolymer was less than 3.2 x 10(4), a well-ordered arrangement of the microsphere and the spherical microdomains of block copolymer in the PS matrix was observed in two dimensions. The degree of order of the spherical microdomain was estimated using the radial distribution function.