The　effect　of　electrostatic　force　on　the　dynamic　response　of　a　Bernoulli-Euler　piezoelectric　nanobeam　is　analyzed　in　this　paper.　The　governing　equations　with　the　electrostatic　stress　are　derived　based　on　a　variational　principle.　Static　bending　problem　of　simply　supported　and　cantilever　beam　is　considered.　The　influence　of　the　electrostatic　force　on　the　first　four　natural　frequencies　is　discussed.　It　is　shown　that　when　the　beam　thickness　is　small,　the　effect　of　the　electrostatic　force　is　significant.　When　the　beam　thickness　is　large,　the　electrostatic　force　is　insignificant　and　can　be　neglected.　The　results　also　indicate　that　one　can　adjust　the　natural　frequency　of　a　nanobeam　by　applying　appropriate　voltage.