Defatted soy flour was mixed at 4, 8, 12 or 16% with buffaloes' milk for preparing yoghurt.  Acidity developed in all the examined blends indicated the suitability of such blends for the growth of yoghurt starter.  Increasing the level of added defatted soy flour resulted in an increase in the content of total solids, total nitrogen, soluble nitrogen and non-protein nitrogen of the resultant yoghurt.  However, fat content declined with the increase in the percent of defatted soy flour.  All of the resultant yoghurt contained no coliform bacteria or Staphylococcus aureus.  But the control yoghurt had higher total bacterial, proteolytic and lipolytic counts compared to the yoghurt made with the addition of soy flour.  Lower total points of sensory evaluation were given to the yoghurt made with the addition of soy flour compared to buffaloes' (control) yoghurt.  Amongst the former, yoghurt containing 4 or 8% soy flour gave scores more similar to those of the control yoghurt.  Addition of 3 or 1.5% butter starter has improved the flavour of such treatments which kept the same trend of chemical composition.