We report the synthesis and magnetic properties of the AgI-intercalated misfit-layer cobalt oxide Bi 1.8 Ca 2 Co 2 O z . The AgI-intercalated Bi 1.8 Ca 2 Co 2 O z was prepared by the guest exchange reaction from the I 2 -intercalated one. SEM-EDX analysis exhibited the stoichiometric ratio of Ag/I and the guest concentration as (AgI)Bi 1.8 Ca 2 Co 2 O z on the basis of Co=2. After the AgI intercalation, the lattice parameter along the c-axis calculated from X-ray diffraction patterns was 21.68 Å, which was drastically increased not only from the non intercalated host phase (14.68 Å) but also from the I 2 -intercalated phase (18.08 Å). After the AgI intercalation, magnetic susceptibility measurements revealed that the antiferromagnetic Weiss temperature and the effective magnetic moment in Co ion simultaneously decreased compared with the non-intercalated host compound.