Abstract: Disclosed are a strainer and a method of injection-moulding the strainer of plastics. A strainer according to this invention comprises a pair of semi-cylindric shells integrally and movably connected along their adjacent longitudinal sides in the state of being developed; top and bottom circular boards integrally connected to the top and bottom frames of one of said semi-cylindric shells; and nets integrally connected to each of said semi-cylindric shells. This developed structure of the strainer makes it possible to injection-mould a semi-product of strainer as a whole in a single injection-mould die, and a so moulded and developed strainer is easily assembled in the final and complete cylindric shape by simply closing the semi-cylindric shells and integrally connecting them along their abutting longitudinal sides.