A new method of measuring low magnetic fields accurately by employing a nuclear quadrupole resonance (NQR) technique in which a hexamethylene–tetramine [(CH2)6N4] crystal is used as the detector is proposed here. By applying the magnetic field (B0) along theZaxis of the electric field gradient tensor at14N in this crystal (&eegr;=0), one14N NQR line (&ngr;0) splits into two lines (&ngr;+and &ngr;−). The difference of these two lines (&dgr;&ngr;=&ngr;+−&ngr;−) is proportional to the applied low magnetic field. Consequently, the magnetic field can be measured with this frequency difference in terms of the nuclear magnetic moment of the14N nucleus. The accuracy, advantages, and limitations of this technique are discussed.