Hexagonal RMnO(3) is known as one of the candidates for multiferroic materials. We have focused on YbMnO(3), which has ferroelectricity along the c axis below 1000 K and antiferromagnetic ordering below 80 K. We have reported that magnetic, field-induced ferromagnetism in YbMnO(3) epitaxial thin films. In this study, we investigate the substitutional effect of the nonmagnetic element, Al, for Mn ions with triangular spin ordering on the ferroelectric and magnetic properties of YbMnO(3).