Preterm infants are at high risk to rapidly become anemic. Therefore, more than 90 percent of infants receive one or more transfusions of red blood cells (RBCs). The objective was to assess if RBC transfusions may induce significant changes of plasma acid-base, electrolytes, and glucose status in preterm infants. We studied infants with gestational age ≤ 34 weeks who were transfused with RBCs at NICU during the first two weeks of life (n = 40). Blood samples were collected from infants before and after transfusions to evaluate hemoglobin (Hb) level, hematocrit, acid-base, electrolytes, and glucose status. Then infants were stratified into two groups according to the volume of transfused RBC. Group 1 includes infants who received a RBC volume of ≤ 20ml/kg while group 2 includes infants who received > 20 ml per kg. Infants received a mean volume of 20.38 (±3.2) ml/kg RBCs. After transfusions, a significant increase of pH (p<0.001), a significant increase of pO2 (p = 0.01), a significant decrease of pCO2 (p<0.001), a significant decrease of Ca+2 (p< 0.001), a significant increase of potassium (p<0.001), a significant increase of hemoglobin(p<0.01), a significant increase of hematocrit (p<0.001), a significant increase of weight(p<0.001), and a significant decrease of heart rate(p<0.001) were observed. Infants who were transfused with > 20 ml/kg (group 2) were significantly more anemic than infants in group1. Infants in group 2 developed more changes than group 1 (more increase of Hb and Hct and more decrease of Ca+2). RBC transfusions were effective in correcting anemia in our patients and induced increase of Hb, Hct, pH, pO2, K+ and decrease of pCO2 and Ca+2. Moreover, infants who received larger volume of RBCs showed a higher increase of Hb, Hct, and decrease of Ca+2.