Most patients with liver cancer are diagnosed when they are not suitable for resection. Although some palliative approaches can be applied to these patients, the overall survival rate remains unsatisfactory. Active hexose correlated compound (AHCC), a newly developed functional food, has been shown to act as a potent biological response modifier in in vitro experiments. Recently, AHCC was found to improve the prognosis of hepatocellular carcinoma patients following surgical treatment. We investigated whether AHCC could prolong survival and improve the prognosis of patients with advanced liver cancer. A prospective cohort study was performed with 44 patients with histologically confirmed liver cancer. All of the patients underwent supportive care. Survival time, quality of life, clinical and immunological parameters related to liver function, cellular immunity, and patient status were determined. Of the 44 patients, 34 and 10 received AHCC and placebo (control) orally, respectively. Patients in the AHCC treated-group had a significantly prolonged survival when compared to the control group by Mann-Whitney test (95% CI, p = 0.000). Quality of life in terms of mental stability, general physical health status, and ability to have normal activities were significantly improved after 3 months of AHCC treatment when tested using the Wilcoxon signed-rank test (on one-sided test, p = 0.028, 0.037, and 0.040, respectively). The apparent different clinical parameters between the two groups were the levels of albumin and percentage of lymphocytes with p-values of 0.000 and 0.026 at 1 and 2 months after treatment, respectively. Unlike the control patients, AHCC treated-patients with longer survival time had the tendency of better outcomes since the levels of AST and ALT had not increased rapidly from their baselines at follow-up. In addition, the levels of total IL-12 and neopterin were slightly increased in AHCC treated-patients. This study suggests that AHCC intake could prolong the survival and improve the prognosis of patients with advanced liver cancer and delay the gradual decline of their physiological status.