Solution-grown lamellar single crystals of bacterial poly[(R)-3-hydroxyvalerate] (P([R]-3HV)) have been prepared in a mixture of chloroform and methanol. P([R]-3HV) crystals were square-shaped and gave well-resolved electron diffraction diagrams from which the reciprocal lattice parameters a* = 1.052 nm(-1), b* = 0.990 nm(-1), and gamma* = 90 degrees could be determined. Systematic absences were confirmed at every odd reflection along the orthogonal axes a* and b* by a series of tilted electron diffraction diagrams. Thus, the electron diffraction pattern is consistent with a pap, symmetry. The diffraction analysis combined with X-ray and electron diffraction diagrams indicated that P([R]-3HV) crystallized in the P2(1)2(1)2(1) orthorhombic space group which had the lattice parameters of a = 0.950 nm, b = 1.010 nm, and c(fiber axis) = 0.556 nm with the a-fold screw symmetry along the molecular axis. The growth planes of P([R]-3HV) single crystals are (110), and the average direction of chain folding determined by polyethylene decoration is parallel to these growth planes. In some cases, the lamellar crystals showed spiral growths originating from screw dislocations with both left-handed and right-handed forms. Lateral force mode image of atomic force microscopy showed the "cross-sector" morphology which was due to differences in the chain-folding direction.