The main goal of this paper is to assess the radiometric stability of the new Sentinel-1A (S-1A) SAR (Synthetic Aperture Radar) sensors. The S-1A radiometric stability was assessed by analyzing the temporal variations of the backscattering coefficient (σ°) returned from invariant targets. The results show three stable sub-time series of S-1A data. The first (between 1 October 2014 and 19 March 2015) and third (between 25 November 2015 and 1 February 2016) sub-time series have almost the same mean σ°-values (a difference lower than 0.3 dB). The mean σ°-value of the second sub-time series (between 19 March 2015 and 25 November 2015) is higher than that of the first and the third sub-time series by roughly 0.9 dB. Moreover, our results show that the stability of each sub-time series is better than 0.48 dB.