Horizontal grafting, in which scion and rootstock are cut at the hypocotyl level transversely, is essential for mechanization of grafting. The present studies have been conducted to improve the survival rate and growth of cucumber grafted on Cucurbita spp. through horizontal grafting at the level of hypocotyls. The survival rate of the cultivar Nankyoku No. 2 (Cucumis sativus) with six vascular bundles at the hypocotyl was different when it was grafted on Unryuh No. 1 or Kongoh (C. moschata) with mainly six vascular bundles. The survival rate of the scion grafted on Dairoku (C. maxima) with mainly 12 vascular bundles was the lowest. It was found that the survival rate was inversely correlated with the difference in the diameters of the hypocotyls of the scion and rootstock. Dry weight value of the surviving scion was larger on Unryuh No. 1 than on Kongoh and the smallest on Dairoku. It is concluded that by minimizing the difference in the diameter of the hypocotyls between the scion and rootstock the survival rate and growth of cucumbers which are horizontally grafted on Cucurbita spp. at the hypocotyl level could be enhanced.