Abstract: This study investigated the effect of maternal undernutrition during late pregnancy on the fetal growth. 100 mongolia ewes allocated to three groups，which were oestrus at scheduled time and become pregnant, were given 0.175 MJME/kgw-0.75d -1 (Restricted Group 1 ;R1), 0.33 MJME/kgw-0.75d-1(Restricted Group 2;R2), and voluntary intake（control group ;CG） respectively during late pregnancy (90-150 d). The results indicated that during feed restriction period(late pregnancy) maternal undernutrition have significant effects on the lamb birth weight（p<0.01）and the average fetal growth rate（p<0.01） of restricted groups, and restricted the body length（p<0.01） and thoracic girth (p<0·01) of R1.The fetal lung（p<0.01）、spleen（p<0.01）、abomasum（p<0.01）、heart （p<0.05） and liver（p<0.05）weight were lighter in R1 than in control group animals， whilst in R2 only the weight of lung（p<0.01）、spleen（p<0.01）was lighter although the weight of other organs expressed a trend to decrease. The fetal brain weight in underfed were not restricted. When expressed as a rate of body weght, the spleen weights in restricted groups were still lighter （p<0.01） than in control group animals, but fetal brain weight in R1 was heavier than in control group（p<0.01）.In a word, maternal undernutrition during late pregnancy have effects on the fetal growth and development.

Key words: late pregnancy, ewes, undernutrition, fetal, growth and development