This paper presents a new measurement technique of relative permittivity (/spl epsi//sub r/) for cable insulators. The travelling wave and reflection wave theory are applied to generate low voltage pulse signal feeding cable lines that need to know /spl epsi//sub r/ of insulators. By measuring the interval of travelling wave, /spl epsi//sub r/ can be estimated for any types of cable lines. A prototype consists of pulse generator circuit, wave detection circuit, counter circuit and microcontroller unit for processing and display via LCD. This model is portable, compact, comfortable and capable of displaying /spl epsi//sub r/ value immediately. From the test results, this model has accuracy within acceptable values.