A 9.5‐GHz electron spin resonance ESR spectrometer which operates in conjuction with a helium dilution refrigerator down to 54 mK is described. Instead of the conventional waveguide and cavity arrangement, coaxial and superconducting twisted pair transmission lines are used to bring the microwave power into the mixing chamber, where a tiny coil surrounds the sample. This lowQ, high‐filling factor configuration has a sensitivity about the same as that of a conventional highQcavity with a small filling factor. Several suggestions for further development and improvement are presented.