Hemoglobin concentrations of single red blood cells are measured by single cell laser tweezers Raman spectroscopy. Hemoglobin solution with different concentrations is prepared and the linear relationship between Raman intensity and hemoglobin concentration is obtained. By detecting the Raman spectrum of a single red blood cell, the hemoglobin concentration of a single red blood cell is calculated according to the linear formula. Raman spectra of 70 red blood cells are measured. The calculated hemoglobin concentration of single red blood cells is from 270 g/L to 500 g/L. Mature erythrocytes account for more than 90% of the red blood cells and its hemoglobin concentration is 350~450 g/L. The hemoglobin concentration of reticulocyte is 300 g/L or less, and the hemoglobin concentration of old red blood cells is higher than 450 g/L. The conclusion conforms to the standard of mean corpuscular hemoglobin concentration (MCHC) 310~370 g/L. Using this method to measure hemoglobin concentration of single red blood cells is quick, non-destructive, simple and accurate. This shows the advantages of Raman spectroscopy on single cell analysis.