Sea ice consists of brine pockets dispersed within solid ice. The orientation, volume fraction and connectivity of these pockets control its physical properties such as thermal energy transport, electromagnetic response and porosity. Monitoring the development of this microstructure is essential to achieve better understanding of sea-ice formation and to model more accurately its climatic role. The brine and ice phase have vastly contrasting electrical responses making it an ideal medium for impedance analysis. Impedance measurements are performed across the frequency range 40 Hz to 1 MHz on laboratory grown sea ice using a custom capacitive cell. The capacitors are deployed in sea water and arranged to monitor the horizontal and vertical impedance. The ice is grown one-dimensionally from the top down enclosing the cells and impedance measurements are made at regular time intervals down to an ice temperature of –25°C. The cell is capable of both four electrode and variable spacing two electrode configurations allowing us to isolate and largely eliminate the contribution of electrode polarization to the measured impedance. This electrode contribution dominates the low frequency measured capacitance up to 500 Hz and is caused by a sharp distribution of salt ions existing at the brine–electrode interface. It is indicative of the amount of brine in contact with the electrode and has been exploited previously in a salinity monitoring system. The true impedance spectrum of sea ice is well represented by a simple RHF + R||C electrical circuit. The high-frequency resistance describes bulk conduction through brine and ice and can be modelled as a simple two-phase conductive mixture with brine volume fraction and geometrical inputs. The parallel RC circuit dominates at low brine volume fractions and describes space charge polarization at brine–ice interfaces and conduction through the interface. This impedance is then strongly related to the surface area of the brine pockets. Analysis is performed on the horizontal and vertical impedance measurements and compared with the observed microstructure of an ice core. The technique offers promise for field application in situ microstructure monitoring.