Harbarnsen is a village and a former municipality in the district of Hildesheim in Lower Saxony, Germany. Since 1 November 2016, it is part of the municipality Lamspringe.
Harbarnsen is situated in an agricultural region between the Weserbergland Schaumburg-Hameln Nature Park and the Harz, roughly 9 km southwest of Bad Salzdetfurth. Surrounding hill ranges, namely Sackwald, Harplage and Heber, are parts of the Lower Saxon Hills.
The municipality of Harbarnsen consisted of two districts, Harbarnsen and Irmenseul.