Background: Malnutrition of inpatients has been associated with higher morbidity, mortality, cost, and longer hospital stay. Total parenteral nutrition (TPN) therapy plays an important role in decreasing morbidity and mortality among critical inpatients in hospitals, and has been commonly used to improve clinical outcomes. However, only a few studies were conducted regarding patients' nutritional improvement by TPN. Method: This study therefore evaluated the changes in nutritional parameters by TPN therapy for early malnourished inpatients. Data from early malnourished inpatients who were treated with TPN therapy between January 2012 and June 2013 at the ${\bigcirc}{\bigcirc}$ university Hospital were studied retrospectively. Information regarding sex, age, underlying diseases, division, TPN (peripheral and central), and changes in nutritional parameters were collected by reviewing electronic medical records. The criteria for evaluation of the changes in nutritional parameters were included physical marker, body mass index (BMI), and biochemical markers, including albumin (Alb), total lymphocyte count (TLC), and cholesterol. Nutritional parameters were collected three times: pre-TPN, mid-TPN and end-TPN. A total of 149 patients (peripheral, 97; central, 52) was evaluated. Results: In all patients, the malnutrition number was significantly decreased following the complete TPN therapy (peripheral patients, pre-TPN: $3.33{\pm}0.12$, mid-TPN : $3.06{\pm}0.17$, and end-TPN: $2.85{\pm}0.21$ (p < 0.05); central patients, pre-TPN: $3.38{\pm}0.11$, mid-TPN: $3.06{\pm}0.13$, and end-TPN: $2.75{\pm}0.21$ (p < 0.05). The malnutrition number means number of nutrition parameters below normal range of malnutrition. In addition, all of the four nutritional parameters (BMI, Alb, TLC and cholesterol) were increased with duration of TPN periods for all patients, and the changes in the early stage were larger than in the late stage (p < 0.05). The nutritional parameters of non-cancer patients were increased to a greater extent compared to cancer patients with longer TPN therapy, but it was not significant. The nutritional parameters of younger patients (50-60 years) were also increased more than of older patients (70-80 years), but it was not significant. Conclusion: In conclusion, the TPN therapy decreases malnutritional status and improves nutritional parameters in malnourished patients, thereby decreasing morbidity and mortality. The combined evaluation of all four nutritional parameters is more accurate for nutritional assessment than a single one.