We observed an apparent diamagnetism in representative quasi-two-dimensional Heisenberg canted antiferromagnets, (C(n)H(2n+1)NH(3))(2)MnCl(4), indicating that the quasi-one-dimensionality is not essential for the apparent diamagnetism. The apparent diamagnetic response seems to be promoted by a thermal quenching and is characterized by a linear response to the applied magnetic field with a constant internal field. (c) 2009 Elsevier B.V. All rights reserved.