Several series of 45 acetophenone derivatives bearing various alkyl or benzyl substituents were conveniently synthesized and their structures characterized by 1H and 13C NMR spectroscopy, HRMS and single-crystal X-ray analysis. Their in vitro antifungal activities against a panel of phytopathogenic fungi were evaluated by mycelial growth rate assay. Of them, 12 derivatives (e.g., 3a–c, 4c and 4e) exhibited more potent antifungal effects on some phytopathogens than a commercial fungicide hymexazol as positive control. In particular, compound 3b with IC50 values of 10–19 μg/mL was found to be the most active in this series and might be a potential lead structure for further optimization. The preliminary structure–activity relationship (SAR) studies of a series of acetophenones are also discussed.