The　Atterberg　limits　and　the　undrained　shear　strength　are　crucial　soil　properties　in　the　preloading　design　of　reclamation　foundation　projects　using　dredged　river　sediment.　These　properties　can　be　significantly　affected　by　the　presence　of　organic　matter　in　the　sediment.　This　study　investigates　the　physical　properties　and　undrained　shear　strength　of　river　sediment,　based　on　data　from　a　series　of　fall　cone　tests　performed　on　river　sediment　with　different　organic　matter　contents,　and　undrained　shear　strength　data　for　reconstituted　clay　collected　from　the　literature.　It　was　found　that　the　liquid　limit,　plastic　limit,　and　plasticity　index　increase　with　an　increase　in　organic　matter　content.　The　effect　of　organic　matter　on　the　undrained　shear　strength　of　remolded　soil　at　a　given　water　content　can　be　attributed　to　the　effect　of　organic　matter　on　the　liquid　and　plastic　limits.　The　undrained　shear　strength　is　a　function　of　the　liquid　and　plastic　limits;　it　can　be　normalized　by　the　liquidity　index,　irrespective　of　the　organic　matter　content.　Highlights　Investigating　role　of　organic　matter　in　the　Atterberg　limits　Investigating　role　of　organic　matter　in　shear　strength　Understanding　key　factors　of　controlling　shear　strength　Establishing　organic　matter–liquidity　index–shear　strength　interrelations.　©　2021　Informa　UK　Limited,　trading　as　Taylor　&　Francis　Group.