Authors:Cruz et alAbstract:Qatar-1b is a close-orbiting hot-Jupiter (Rp≃1.18 RJ, Mp≃1.33 MJ) around a metal-rich K-dwarf, with orbital separation and period of 0.023 AU and 1.42 days, respectively. We have observed the secondary eclipse of this exoplanet in the Ks-band with the objective of deriving a brightness temperature for the planet and providing further constraints to the orbital configuration of the system. We obtained near-infrared photometric data from the ground by using the OMEGA2000 instrument at the 3.5 m telescope at Calar Alto (Spain), in staring mode, with the telescope defocused. We have used Principal Component Analysis (PCA) to identify correlated systematic trends in the data. A Markov chain Monte Carlo analysis was performed in order to model the correlated systematics and fit for the secondary eclipse of Qatar-1b using the occultation model by Mandel & Agol (2002). We measured a secondary eclipse depth of 0.196%+0.071%−0.051%, which indicates a brightness temperature in the Ks-band for the planet of 1885+212−168 K. We also measured a small deviation in the central phase of the secondary eclipse of −0.0079+0.0162−0.0043, which leads to a value for ecosω of −0.0123+0.0252−0.0067. However, this last result should be confirmed with more data. This work highlights that ground-based secondary eclipse observations are capable of providing useful constraints on the orbital configuration of bright, giant planets that can be used to probe the architecture and multiplicity in hot Jupiter systems.