Crystal structure of Staphylococcal β-ketoacyl-ACP reductase 1 (SaFabG1) complexed with NADPH is determined at 2.5 Å resolution. The enzyme is essential in FAS-II pathway and utilizes NADPH to reduce β-ketoacyl-ACP to (S)-β-hydroxyacyl-ACP. Unlike the tetrameric FabGs, dimeric SaFabG1 shows positive homotropic cooperativity towards NADPH. Analysis of FabG:NADPH binary crystal structure endorses that NADPH interacts directly with the helices α4 and α5 those are present on a dimerization interface. A steady shift in tryptophan (of α4 helix) emission peak upon steady increment of NADPH concentration reveals that the dimeric interface is formed by α4-α4' and α5-α5' helices. This dimeric interface imparts positive homotropic cooperativity towards NADPH. PEG, a substrate mimicking molecule is also found near the active site of the enzyme. Proteins 2012; © 2011 Wiley Periodicals, Inc.