We present a method for fabrication of concave polydimethylsiloxane (PDMS ) microlens array. A digital maskless grayscale lithography system based on digital micromirror device (DMD) is established. Microlens array with a square base is fabricated in photoresist by the system, which is used as replication model. By replica molding technique, a concave PDMS microlens array with a square base is fabricated. Experimental and test results show that the edges of PDMS microlenses are clear, the surfaces are smooth, and the spotlight performances are favorable. The light intensities which transit the microlens array are uniform. The approach described in the paper is a new method for fabrication of concave PDMS microlens, which has advantages of facile, effective, low cost, and arrays can be replicated by larger scale.