Crystals of GdFe3-xGax(BO3)(4) family were grown. Their structure at x= 0.9 is established by single crystal X-ray diffraction. Field, temperature and orientation dependencies of magnetization are presented. The influence of substitution by Ga3+ in Fe helicoidal chains is analyzed. The magnetic structure model is presented. (C) 2003 Elsevier B.V. All rights reserved.