Abstract： Objective To study effects of beta cell dysfunction and insulin resistance on the pathogenesis of type 2 diabetic families. Methods Oral glucose tolerance test (OGTT), insulin and true insulin secretion test, as well as the assays of blood triglyceride (Tg), cholesterol (Ch), low density lipoproteins (LDL C) and high density lipoproteins (HDL C) were performed in a total of 218 adult subjects (over 20 years of age) from 23 type 2 diabetic families. The study was consisted of 128 non diabetic first degree relatives (group A), 23 patients with impaired glucose tolerance (group B), 51 diabetic patients diagnosed previously (group C), and 16 diabetic patients diagnosed newly (group D) ,and 59 healthy subjects without diabetic families and with normal OGTT (group E). Results Levels of serum LDL C in Group A and B were higher than that in group E, levels of serum LDL C, TG and TC in group C and D were higher than that in group E. Each level(except 30 min )of immunoreactive insulin at OGTT in group A,B and D was higher than that in group E. Secreting peak times in groups A and E were at 60 min of OGTT, but those in group B, C and D were all at 120 min. The true insulin levels at fasting and 30 min in the OGTT(only 30 min at OGTT in group A)in group A and B were lower than that in group E. Each level of true insulin at OGTT in group C and D was lower than that in group E.IR indexes in group A, B, C and D were all higher than that in group E. HOMA β in group B,C and D were all lower than that in group E. Conclusions There is metabolic abnormality of blood lipid, and insulin resistance in non diabetic first degree relatives of type 2 diabetic families. There is both insulin resistance and islet secretion dysfunction in patients with impaired glucose tolerance. There is critical islet dysfunction in previously and newly diagnosed diabetic patients.