[Zn-2(Oxac)(Taz)(2)]center dot(H2O)(x), referred to as ZOTW(x), was prepared from aqueous methanol solutions of Zn-5(CO3)(2)(OH)(6) and two kinds of ligands, 1,2,4-triazole (Taz) and oxalic acid (Oxac), at 453 K under magnetic fields of up to 6 T. The magnetic fields markedly changed the morphology from irregular agglomerates at zero field to rectangular-prism crystals having smooth surfaces at 6 T, although the monoclinic crystal structure was only slightly deformed to a triclinic one. As-synthesized ZOTW(x)(H)) prepared under magnetic fields of H/T >= 2 adsorbed a large amount of N-2 at 77K in rectangular Type I adsorption isotherms even without the usual pretreatment at 383 K and 1 mPa. It suggests that high magnetic fields induced the formation of hydrophobic micropores having uniform sizes. The hydrophobicity was consistent with the results that the water-assisted micropore formation was depressed in the as-synthesized ZOTW(x)(H)) containing a small amount of water.