The title complex, [MnHg(SCN)4(CH4N2O)3]n, consists of slightly distorted octahedral MnN3O3 and tetrahedral HgS4 units. The Mn(II) atom is coordinated by the O atoms of three urea molecules and by the N atoms of three SCN- ions; Hg(II) is coordinated by four S atoms from SCN- ions. Each pair of Mn(II) and Hg(II) atoms is connected by an -SCN- bridge, forming infinite two-dimensional -Mn-NCS-Hg- networks.