The aim of this study was to assess the levels of serum 1,25dihydroxycholecalciferol and its relation to bone mineral density andheart disease in beta thalessmia patients.Methods: Eighty patients with B-thalassemia major with a mean age16 years (range 10 – 22years), underwent full history taking, clinicalexamination and laboratory tests including complete blood count, calcium, phosphorus, alkaline phosphatase, Serum ferritin and serum 1,25Dihydroxycholecalciferol.Complete M-mode and pulsed Doppler echocardiography were performedfor cases to study diastolic and systolic functions and measurements wereobtained. Myocardial Performance Index (MPI) was calculated for boththe left and right ventricles ,and data was interpreted.Bone mineral density (BMD) (g/cm 2) was measured at lumbar spine(L1–L4), radial and femoral area using dual-energy x-ray absorptiometry(LUNAR, DPXMD#7164).T scores and Z scores will be used.Results: Among our cases sixteen patients (20%) had low serum1,25 dihydroxycholecalciferol level, 4 (5%) had an increased level whilethe remaining 60 patients(75%) had normal levels, Those who are below18 years, we measured their bone density by Z score, 60 patients (94%)had decreased bone density and 4 patients(6%) had normal bone mineraldensity while those who are above 18 years, we measured their bonedensity by T score ,13 patients (81%) had decreased bone density ,3patients(19%) had osteopenia, There was no statistically significantcorrelation between 1.25 (OH)2 Cholecalciferol and bone density, Therewas a statistically significant positive (direct) correlation between 1,25X(OH)2 Cholecalciferol and Calcium, There was a statistically significantnegative (inverse) correlation between 1,25 (OH)2 Cholecalciferol andPhosphorus; and alkaline phosphatase. There was no statisticallysignificant correlation between 1.25 (OH)2 Cholecalciferol and cardiacdysfunction.Conclusion: There is no association between 1,25 dihydroxycholecalciferol and myocardial dysfunction .And also there is noassociation between 1,25 dihydroxycholecalciferol and bone mineraldensity in pediatric patients with beta-thalassemia major