A paper lunch box includes a box body, at least one longitudinal partition member and at least one transverse partition members respectively installed in the box body to support the box body in shape and to separate the holding space of the box body into separated compartments, the box body being formed of a patterned cardboard folded up into a rectangular container having vertical peripheral walls of double-layer construction, the transverse and longitudinal partition members being formed of a respective patterned cardboard, each having a .andgate.-like cross section and reinforcing end flaps for mounting.