The single-cell-molecular technique based on optical tweezers and Raman spectroscopy is employed to study single reticulocytes and small lymphocytes of Sprague Dawley (S.D.) rat in nearly physiological solution. The spectra of single reticulocytes and small lymphocytes are obviously different due to their components. The main differences show that characteristic Raman bands of the protein are 1212, 1548, 1607 and 1616 cm-1 for reticulocytes, 1001 and 1661 cm-1 for small lymphocytes, and that of nucleic acid is 1584 cm-1 for both of them. The content of nucleic acid of small lymphocytes is more than that of reticulocytes, but for protein it is reverse by the histogram analysis of part characteristic Raman bands. Furthermore, the reticulocytes and small lymphocytes can be distinguished completely by principal component analysis and discriminant function analysis. The way of distinguishing quickly and accurately of single reticulocytes and small lymphocytes by the Raman spectra cannot be realized by optical microscope. It also provides a new method to distinguish two kinds of cells in blood for modern biomedicine study.