Two greenhouse experiments were conducted to evaluate the nematicidal activity of certain alkaloid plants namely, periwinkle (Catharunthus roseus), datura (Datura stramonium), lupin (Lupinus albus), pomegranate (Punica granatum) and fenugreek (Trigonella foenum-graecum) against root-knot nematode, Meloidogyne incognita infecting cucumber (Cucumis sativus) and reniform nematode, Rotylenchulus reniformis infecting cantaloupe (Cucumis melo var.cantaloupensis). Dried powedered parts of such plants were screened at three rates (1, 3 and 5g / plant).  In most treatments data indicated a positive correlation between tested rates and plant biomass. Meanwhile, dried leaf powder of C. roseus (62.5%) as well as dried seed powder of  L. albus ( 52.8%), and T. foenum-graecum ( 43.2 %)  induced remarkable improvement in total plant fresh weight of cucumber at the rate of 5g / plant. However, dried leaf powder of D. stramonium (41.4%) recorded a significant increase in total plant fresh weight at the rate of 3g / plant.  By all treatments of alkaloid plants root-knot nematode population whether in soil and roots, root galling and number of egg masses were significantly suppressed.  Dried leaf powder of C. roseus at three tested rates (71.8, 71.6 and 72.6%) performed the best and suppressed total nematode population of M. incognita  followed by T. foenum-graceum at 5g / plant (70.1%). On the other hand, a slight to moderate improvement in plant growth parameters of cantaloupe infected with R. reniformis was indicated in pots receiving alkaloids plants. The highest percentage of increase in total plant fresh weight was noticed with dried leaf powder of C. roseus at three tested rates (28.5, 31.4 and 32.6%) respectively. The best protection of cantaloupe against R. reniformis was recorded with dried seed powder of T. foenum-graecum (57.9, 65.2 and 75.0%) and P. granatum( 55.4, 55.9 and 61.7%) at three tested rates, respectively which ultimately suppressed R. reniformis population.