This article represents the study of safety and efficiency of intraoperative photodynamic peritoneal therapy (IOPDT) developed in P.A. Herzen Moscow Cancer Research Institute. IPPDT was performed in 84 patients with locally advanced and disseminated gastric cancer. The control group included 100 patients with surgical treatment only. All patients underwent subradical or palliative subtotal distal gastroectomy or total gastrectomy with D2, D3 lymph node dissection. For IOPDT group Photohem was administrated intravenously in dose 2,5 mg/kg 48 h prior to operation, the session of peritoneal irradiation was performed after completion of the surgery (with laser device LFT-630-01 «Biospec», wavelength 630nm, light dose 6 J/cm²). IOPDT of peritoneum was associated with good tolerance, did not increase the rate and severity of post-operative complications. The efficiency of IOPDT was assessed with adjusted survival rates in study and control groups by Kaplan-Meier analysis. IOPDT significantly improved the prognosis in patients with subradical treatment, with metastasis in less then 15 lymph nodes. The use of IOPDT after surgery in this group of patients contributed to increase of median survival rate from 29.3 up to 43.6 months, annual survival rates from 80.0±5.7% to 93.7±4.2%, 3-year survival rates from 45.5±7.6% to 82.1±7.1%. Accordingly, IOPDT did not improved outcomes for palliative surgery R1–R2 and in patients with more than 15 involved lymph nodes.