The dimensional instability of a paper sheet induces curl and cockling in moisture changes. All elements of a paper making process that have influence on dimensional stability of the produced paper sheet, are potential sources for undesired flatness deviations. The most probable sources are pulp properties, fiber orientation angle and its anisotropy, basis weight variations, fines and fillers variations, drying stresses and moisture nonuniformities. However, it is not clear what is the significance of these factors in different situations. In this paper a continuum mechanical model is used to research the effect of fiber orientation angle and its anisotropy to the cockling of a paper sheet. As a result it is shown that these two factors have a great correlation to the paper cockling.