Left ventricular hypertrophy (LVH) is an important marker of cardiovascular risk, while malnutrition is common among adults. The Controlling Nutritional Status (CONUT) score is an objective tool for nutritional assessment. This study aimed to investigate the associations of CONUT-defined nutritional status with LVH and reduced left ventricular ejection fraction (LVEF) in adults. This single-center retrospective cross-sectional study included 2066 adults. Nutritional status was classified according to the standard CONUT categories as normal nutrition, mild malnutrition, and moderate/severe malnutrition. Echocardiography was used to assess left ventricular mass index and LVEF, and LVH was defined using sex-specific left ventricular mass index thresholds. Logistic regression analyses were performed to evaluate the associations of CONUT-defined nutritional status with LVH and reduced LVEF. Among the 2066 participants, 1002 (48.5%) had normal nutritional status, 912 (44.1%) had mild malnutrition, and 152 (7.4%) had moderate/severe malnutrition. In the multivariable logistic regression model, both mild malnutrition (odds ratio [OR] = 1.597, 95% confidence interval [CI]: 1.033–2.495; P = .037) and moderate/severe malnutrition (OR = 2.810, 95% CI: 1.445–5.223; P = .002) were independently associated with higher odds of LVH. Moderate/severe malnutrition was independently associated with reduced LVEF (OR = 2.350, 95% CI: 1.259–4.239; P = .006). Poorer CONUT-defined nutritional status was associated with a higher prevalence of left ventricular structural and functional abnormalities. CONUT-defined nutritional status may provide supplementary information for cardiovascular risk stratification.