This paper reports on the use of arrays of nanoelectrodes as implantable sensors to wirelessly measure the activity of the Sympathetic Nervous System - Sympathetic Nervous Activity (SNA). SNA can be measured as a train of electrical pulses. Traditionally, SNA has been measured with wire electrodes. These measurements have not been easy because of poor signal-to-noise ratio (SNR). In the current work, we have successfully demonstrated improved SNR of SNA measurements achieved by the use of novel Planar Nanoelectrode Arrays (PNAs) in a chronic setting. The PNAs are placed on the left stellate ganglion (SG) via a thoracotomy. Nano scale features on the electrodes provide increased contact area with the nerve of interest (in this case the SG) thereby reducing the limiting (Johnson) noise. The PNAs were fabricated using standard CMOS compatible fabrication techniques on a high resistivity silicon substrate. After suitable wire-bonding and packaging, the PNAs were placed on the left stellate ganglion of a canine test subject. For adequate comparison, a standard set of wire electrodes were embedded on the same nerve in close proximity of the PNAs. Both the sensors were connected to a wireless transmitter (Model No. TR 70BB) powered with a rechargeable battery also placed within the canine test subject. The thoracotomy incision was repaired and the canine test subject allowed to recover before beginning SNA measurements. Our results showed that the PNAs consistently exhibit superior SNR of the measured SNA. Measurements have been successfully made up to three months after implantation of the electrodes and the SNR of the PNA has been consistently better than the wire electrodes. After one month the SNR of the PNA was 48.54 ± 2.71 dB vs. 17.88 ± 4.49 dB for the wire electrode (p < 0.001). At three months the SNR of the PNA was 48.57 ± 1.63 dB vs. 18.98 ± 2.38 dB for the wire electrode (p < 0.001).