This study was conducted during the two successive seasons of 2005 and 2006 at the Experimental Farm of El-Kassasin Horticultural Research Station, Ismailia Governorate, using periwinkle plant (Catharanthus roseus, L. G. Don cultivar) to study the effect of nitrogen sources, humic acid concentrations and their interactions on growth and the content of alkaloids determined as perivine.    Plants raised in sand culture and irrigated with complete nutrient solution contain five different ratios of nitrate – N to ammonium – N and four different concentrations of humic acid.      Greatest growth measured by plant height (cm), stem diameter (cm), number of branches/plant, number of leaves/plant, root main length (cm), fresh and dry weights of branches (g)/plant, fresh and dry weights of leaves (g)/plant,  fresh and dry weights of roots (g)/plant, N.P.K. % and content of alkaloids occurred at the highest ratios of nitrate – N to ammonium – N . Similar trend was obtained with 200 ppm humic acid.