Abstract : Vitamin D deficiency and mentality dysfunction are common in low Glomerular Filtration Rate GFR in dialysis and non-dialysis patients, low level of vitamin D most lyrelated to hypertension, neurocognetionimperment, muscle weakness, hyperlipidemic, diabetes, and cardiovascular disease. Mentality domains impairment remains undiagnosed and undermanaged in chronic kidney disease CKD patients. The level of vitamin D clinically estimated by scaling the vitamin D status which is determined clinically by measuring the 25(OH)D vitamin level that circulating within body. Levels of vitamin D ranging within 30-80 ng/ml are considered optimum level, vitamin D level which evaluated as a suboptimal is further classified into deficiency and insufficiency where the susceptible to develop CKD at vitamin D deficiency. Low level of vitamin D associated with mentality dysfunction especially in hemodialysis patients but the link is still not completely cleared. Assess mentality domains defectiveness using one validated score: monumental state examination in patients with low GFR, with or without hemodialysis. A total of 63 patients with no dialysis CKD and 68 patients on scheduled hemodialysis have been included in this study in which CKD was defined as GFR<60 ml/min using MDRD equation. Exclusion criteria: <20 years, pregnant women, deaf patients, low education, and CVA patients. Mentality test have been done for all patients (CKD and ESRD) by using monumental state examination test which measures mentality (mentality) functions with a components of orientation, attention, recall, and language with score >24 (out of 30). Vitamin 25(OH) D-level assessed from each subject using enzyme immunoassay method with assay range from 40-110 ng/ml. for dialysis patients 36.8% had different 25(OH) D-level, while 40.2% had insufficient level, and 22.8 had sufficient vitamin D level. Serum level of 25(OH)D-level was significantly lower in patients on dialysis compared with CKD patients. Minimental status examination score was lower significantly in hemodialysis patients compared to non-dialysis patient. There was significant correlation between various mentality domains test (MMs) and vitamin D levels. there was high prevalence of 25 (OH) D deficiencies in patients with low GFR especially on hemodialysis associated with poor mentality domains