The present invention relates to a metformin extended release tablet, particularly to a metformin extended release tablet comprising metformin, which is effective in treating non-insulin dependent diabetes mellitus, as active ingredient, and a matrix in which hydrophilic polymers and hydrophobic materials are mixed at a specific proportion. The hydrophilic polymers enable controlling of the pore size of the gel layer formed by water swelling, thereby enabling primary control of drug release rate. And, the hydrophobic materials block the pores of the gel layer, thereby enabling secondary control of drug release rate. Therefore, the metformin extended release tablet of the present invention has better dissolution properties than conventional extended release tablets and, thus, enables extended drug release at constant rate even with less matrix. A constant blood level can be maintained with one administration a day and the tablet can be made smaller, which makes the administration easier and the production simpler.