A modular fan includes a casing and a heat dissipating module. The casing includes an outer frame, a first accommodating chamber and a second accommodating chamber, and the first and second accommodating chambers are disposed at both ends of the casing. The outer frame and the first and second accommodating chambers are integrally formed. The heat dissipating module includes a first fan and a second fan, and the first and second fans are accommodated in the first and second accommodating chambers respectively; four endpoints of the diagonals of the outer frame have a fixed portion. separately Compared with the conventional single fan required to be installed on a 240 mm-radiator one by one, the modular fan of the present invention can be installed on the 240 mm-radiator directly to reduce the inconvenience of installation. In addition, the invention provides a better heat dissipating efficiency than the conventional single fan.