We fabricated square diffractive microlens array with five staircases in the THz wave band for Nb5N6 microbolometers. With each microlens intergrated with an Nb5N6 microbolometer on the same substrate, an array chip was fabricated in the 4 inches silicon wafer. The lens exhibits good focusing and improves the coupling efficiency. The voltage response of the microbolometer integrated with diffractive microlens is 16 times higher than that of the microbolometer fabricated on silicon substrate. The microbolometers used as room-temperature detectors yield a good responsivity of 71 V/W and a noise equivalent power of 1.0 × 10-10 W/Hz. The diffractive microlens array features light weight, low absorption loss, and high resolution and can be mass produced using standard micro-fabrication techniques.