Introduction & Objective: cancer treatment relate fatigue is the most prevalent and distressing side effect of treatment for cancer patients .fatigue lead to decline emotional ,psychosocial  and physical functions and can be influence on the individual's quality of life.

The purpose of this study was determine the intensity of fatigue in cancer patients before and after 3 cycle chemotherapy in selected hospitals of Tehran and shahid beheshty medical science university in 2001-2002.

Materials & Methods: This is adiscriptive –correlative study that utilized a purposeful sampling .one hundred twenty one out patients with cancer participated in this study.data callectad by interview .the instruments used included: the sample selection and demographic data form, social support questionnaire, fatigue severity scale , piper fatigue scale and quality o life scale (qol-30)

Results: The finding indicated that a significant different between mean of intensity of fatigue(P<0.001) before and after 3 cycle chemotherapy .significant different  was found between changes of intensity of fatigue with hope and uncertainty (P<0.001)  and  BMI(P=0.008),and significant positive correlation was found between intensity of fatigue with Hb and distressing symptom ( P<0.001).

Conclusion: in cancer patient intensity of fatigue increase over the course of chemotherapy . Loss of BMI, other side effects ,hopeless , uncertainty ,anemia lead to increase intensity of fatigue . Fatigue lead to decline emotional ,psychosocial  and physical functions and can be influence on the individual's quality of life.  The nurses by appropriate intervention and patient's education   about self care intervention  can help to reduce fatigue and improve quality of life