Electric birefringence was determined by rectangular and reversing pulse methods. Dipole moment of tropomyosin in salt-free solution is extrapolated as 390 Debye units in neutral solution which indicates a complete depolymerization upon infinite dilution. The results on the relation between tropomyosin concentration and birefringence implies the reversible linear polymerization by 3 ways: head-to-tail; head-to-head; side-by-side. Above 30cC or in acid (< pH 6) and in alkaline (>pH 9) tropomyosin is markedly depolymerized.