The magnetic properties of the HfFe6Ge6-type Gd1-xTmxMn6Sn6 (0 <= x <= 0.9) compounds have been investigated in the temperature range of 5-600 K. The compounds with x <= 0.8 are ferrimagnetic in the whole temperature range. The ferrimagnetic Curie temperatures decrease with increasing Tin content from 435 K (x = 0) to 344 K (x = 0.9). The samples with x = 0.85 and 0.9 show paramagnetic-ferrimagnetic-antiferrimagnetic-ferrimagnetic phase transitions with decreasing temperature. For the x = 0.85 compound, the metamagnetic phase transition from antiferromagnetism to ferrimagnetism is induced by an applied field 20 kOe. (c) 2005 Elsevier B.V. All rights reserved.