Horizontal grafting, in which scion and rootstock are cut and grafted horizontally at the hypocotyls, is essential for mechanization of grafting. The present studies have been conducted to improve the survival ratio and the growth of cucumbers grafted on Cucurbltaspp. through horizontal grafting at the hypocotyls. The survival ratio of `Nankyoku 2' (Cucumissativus) which had six vascular bundles at the hypocotyl was different when it was grafted on `Unryuh' or 'Kongoh' (C. moschata), six vascular bundles. The survival ratio of the scion grafted on `Dairoku' (C. maxima) which had twelve vascular bundles was the lowest. It was found that the survival ratio inversely correlated with the difference in the diameters of the hypocotyls of the scion and the rootstock. Fresh and dry weights of survival scions on `Unryuh' and `Kongoh' were almost same and heavier than that on `Dairoku'. It is suggested that minimizing the differences in the diameters and the numbers of the vascular bundles of the hypocotyls between the scion and the rootstock promotes the survival ratio and the growth of cucumbers which are horizontally grafted on Cucurbitaspp..