Nanofibers have enormous applications in various areas such as environment, new energy, National security, filtration and so on. In this paper, polyvinyl alcohol micro-porous webs with excellent properties and highly filtration efficiency are fabricated using electrospinning. The solvent chosen is anhydrous formic acid and formic acid with concentration of 88 wt%. Filtration efficiency of fabrics strongly depends upon fiber size and pore size. A mathematical relationship between filtration efficiency and pore size is suggested.