<p>Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic <sup>10</sup>Be concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (< 250 µm) than typically analyzed in <sup>10</sup>Be studies, and few studies have measured <sup>10</sup>Be concentrations in quartz grains smaller than 100 μm or assessed the impacts of mixing, grain size and interannual variability on the <sup>10</sup>Be concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic <sup>10</sup>Be concentrations of quartz grains in the 50–100 and 100–250 μm size fractions of sediments from the Var basin (southern French Alps) to test the reliability of denudation rates derived from <sup>10</sup>Be analyses of fine sands. The Var basin has a short transfer zone and highly variable morphology, climate and geology, and we test the impact of these parameters on the observed <sup>10</sup>Be concentrations. Both analyzed size fractions returned similar <sup>10</sup>Be concentrations in downstream locations, notably at the Var's outlet, where concentrations ranged from (4.02 ± 0.78) × 10<sup>4</sup> to (4.40 ± 0.64) × 10<sup>4</sup> atoms g<sub>quartz</sub><sup>−1</sup>. By comparing expected and observed <sup>10</sup>Be concentrations at three major river junctions, we interpret that sediment mixing is efficient throughout the Var basin. We resampled four key locations one year later, and despite variable climatic parameters during that period, interannual <sup>10</sup>Be concentrations were in agreement within uncertainties, except for one upper subbasin. The <sup>10</sup>Be-derived denudation rates of Var subbasins range from 0.10 ± 0.01 mm yr<sup>−1</sup> to 0.57 ± 0.09 mm yr<sup>−1</sup>, and spatial variations are primarily controlled by the average subbasin slope. The integrated denudation rate of the entire Var basin is 0.24 ± 0.04 mm yr<sup>−1</sup>, in agreement with other methods. Our results demonstrate that fine-grained sediments (50–250 µm) return accurate denudation rates and are thus suitable targets for future <sup>10</sup>Be applications, such as studies of paleo-denudation rates using offshore sediments.</p>