Abstract: A recent investigation of the low temperature properties of the paramagnetic heavy fermion system CeRuSi revealed an anomalous decrease of the coefficient C/T below 6 K, indicating a second low energy scale well below the Kondo temperature of about 50 K. We started an investigation of this unusual behavior using the local probe ²⁹Si-NMR. Here a preliminary ²⁹Si field sweep NMR study in the temperature 4.2-200 K is reported. ²⁹Si-NMR powder spectra obtained at 72.9 MHz could be simulated and shift components ²⁹K_ab(T) and ²⁹K _c(T) were determined. The shift along the basal plane ²⁹K_ab(T) shows the expected behavior with a Curie-Weiss dependence at high T merging in a constant value below 15 K. In contrast the shift along the tetragonal axis reveals an anomalous T dependence below 15 K where ²⁹K_c(T) drops by a factor of 2, confirming the presence of a further low T energy scale. We suspect this drop to be related to the anomalous decrease of C/T below 6 K and discuss possible mechanism. © 2010 IOP Publishing Ltd.