Two mercury selenite compounds HgM-(SeO3)(2)(H2O)(2) (M = Co, Ni) are synthesized using a conventional hydrothermal method. Both compounds crystallize in the monoclinic structure with a C2/c space group, and equivalent Co2+ or Ni2+ ions exhibit a stacked triangular lattice. Magnetic measurements suggest different magnetic properties between these two isostructural compounds, in which HgCo(SeO3)(2)(H2O)(2) undergoes a canted antiferro-magnetic order below T-N = 7.6 K, while HgNi(SeO3)(2)(H2O)(2) exhibits a collinear antiferromagnetic order below T-N = 9.0 K. When applying a magnetic field, two successive magnetic transitions are observed at B-c1 similar to 1 T and B-c2 similar to 3.6 T in HgCo(SeO3)(2)(H2O)(2), whereas only one field-induced transition is detected around 3.1 T in HgNi(SeO3)(2)(H2O)(2).