Abstract: Abstract: The aim of this study was to obtain the optimum proportion of peat and vermiculite to composted corncob / bagasse for a good growing media in cucumber seedling. The corncob was common in the north of China, while the bagasse was common in the south of China. This experiment studied the influence of the physical and chemical properties of different treatments on cucumber seeding. Four treatments were set with corncob: T1 (all was corncob), T2 (corncob:vermiculite=1:1, v/v), T3 (corncob:peat=1:1, v/v) and T4 (corncob:vermiculite:peat=1:1:1, v/v). Bagasse was also used to set 4 treatments: T5 (all was bagasse), T6 (bagasse:vermiculite=1:1, v/v), T7 (bagasse:peat=1:1, v/v) and T8 (bagasse:vermiculite:peat=1:1:1, v/v). And we took 'Zhongnong 26' cucumber (Cucumis sativus L.) as experimental material and traditional commercial substrate as control. The experiment was carried out in the greenhouse of Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences from September to October in 2014. The parameters included bulk density, pH, electrical conductivity (EC), total porosity, water holding capacity, air filled porosity and nutrition content of different substrates, and cucumber height, stem diameter, ground fresh weight, ground dry weight, underground fresh weight, underground dry weight and seedling index. Bulk density, porosity and nutrition were determined by the methods of Bao and Lian. The pH value and EC were determined by IQ150 Portable pH/mV/thermometer measurement. The parameters of cucumber were determined by conventional method. The results indicated that: T4 and T6 could meet the requirement of cucumber seedling culture. The cucumber heights of T4 and T6 were 15.06 and 22.17 cm, respectively. The stem diameters of T4 and T6 were 4.03 and 3.97 mm, respectively. The ground fresh weights of T4 and T6 were 5.01 and 4.63 g, respectively. The dry weights of T4 and T6 were 0.94 and 1.19 g, respectively. T4 and T6 had a significant influence on the height and stem diameter of cucumber, which were better than the control. And the ground fresh weights and ground dry weights of T4 and T6 had no significant difference with the control. The underground fresh weights of T4 and T6 had no significant difference with the control, but T4 and T6 were significantly better than any other treatment. T6 had no significant difference on underground dry weight compared with the control. And the seedling index of T6 had no significant difference with the control. The seedling index of T4 had significant difference with the control (P<0.05), and was better than any other treatment which included corncob (P>0.05). The comprehensive evaluation coefficient of T6 was better than any other treatment and control. The comprehensive evaluation coefficient of T4 was better than any other treatment which included corncob, and there was no obvious difference between T4 and control. So we concluded that T4 and T6 were horticulturally acceptable as an alternative to commercial substrate for cucumber seedling culture.