Patients after gastrectomy for gastric cancer are at risk of malnutrition, and poor nutritional status negatively affects patients’ clinical outcomes. Knowledge of the factors influencing patients’ nutritional status can inform interventions for improving patients’ nutrition. A cross-sectional study was conducted to describe nutritional status and related factors in gastric cancer patients after gastrectomy. A convenience sample of gastric cancer patients with gastrectomy was recruited from general surgery or oncology clinics of a medical center in northern Taiwan. Data were collected with self-reported questionnaires, including the Functional Assessment Cancer Therapy—Gastric Module version 4, the Concerns in Meal Preparation scale, the Center for Epidemiologic Studies Depression Scale, and the Mini Nutrition Assessment. One hundred and one gastric cancer patients participated in the study. There were 81 cases of subtotal gastrectomy and 20 cases of total gastrectomy. Most patients (52.5%) were malnourished or at risk. Linear regression showed that symptom severity (β = −0.43), employment status (β = 0.19), and difficulty in diet preparation (β = −0.21) were significant predictors of nutritional status. Together, these three variables explained 35.8% of the variance in patient nutritional status (F = 20.3, p < 0.001). More than 50% of our participants were malnourished or at risk for malnutrition, indicating a need for continued monitoring and support after discharge from hospitals. Special attention should be given to patients with severe symptoms, unemployment, and difficulties in diet preparation.