In　an　underdeveloped　remanufacturing　system,　poor　infrastructure　and　low　technical　level　impede　further　development　of　remanufacturing.　To　overcome　this　obstacle,　a　huge　amount　of　fixed　investment　is　required　to　improve　the　remanufacturing　system.　However,　this　investment　inevitably　influences　the　manufacturer＇s　manufacturing/remanufacturing　decision-making　economically.　The　relationship　between　fixed　investment　and　recycling　ratio　was　investigated,　and　the　two-and　multi-period　manufacturing/remanufacturing　mixed　optimization　models　were　developed.　Based　on　the　Karush-Kuhn-Tucker　(KKT)　conditions,　the　optimal　manufacturing/remanufacturing　and　fixed　investment　policies　were　obtained　in　closed-form　expressions.　Moreover,　the　influences　of　the　fixed　investment　were　analysed.　Results　show　that　the　optimal　policies　are　significantly　influenced　by　the　degree　of　underdevelopment　of　the　remanufacturing　system.　When　the　remanufacturing　system　is　underdeveloped,　the　manufacturer　shows　a　lack　of　enthusiasm　in　remanufacturing,　thereby　resulting　in　the　decrease　of　the　investment　and　the　recycling　ratio.　The　manufacturer　raises　the　sale　price　to　alleviate　the　loss　caused　by　fixed　investment,　but　the　total　manufacturing　quantity　and　profit　decrease.　In　the　multi-period　case,　the　manufacturer　gradually　increases　the　investment　for　continuously　improving　the　remanufacturing　system　to　increase　the　recycling　ratio　and　obtain　additional　profits　from　remanufacturing.　The　proposed　models　can　effectively　provide　the　reference　for　determining　the　reasonable　manufacturing/remanufacturing　and　fixed　investment　policies　in　the　underdeveloped　remanufacturing　system.