The aim of this work was to evaluate the potential of certain soil organic matters i.e. poultry or horse manures or dried-leaf powders of periwinkle (Chatharanthus roseus) or castor (Ricinus communis) in comparison with oxamyl againstMeloidogyneincognitaon Egyptian cotton cv. Giza 45 in vivo. Five grams of each soil organic amendments were separately added to cotton seedlings cultivated in pots, as well as oxamyl at the recommended dose, one day before nematode inoculation process. Results revealed that all tested materials significantly improved plant growth parameters and reduced nematode population density, number of galls, females and egg-masses on roots of cotton plants. Of the tested organic matters, poultry manure achieved the highest percentage increase in plant length, shoot dry weight and fresh weight of whole plant with values of 54.4, 74.7and 37.2%, respectively, followed by perwinkle powder for the first two parameters with values of 51.0 and 65.9%, respectively, whereas, castor powder for the later parameter with value of 44.7% as compared with nematode alone. Moreover, oxamyl treatment ranked first in percentage increase values of shoot dry weight (87.9%) and fresh weight of whole plant (62.5%), respectively, and second to poultry manure treatment with value of plant length (58.0%) comparing to nematode alone. In addition, non- significant differences between all tested organic matters regarding nematode parameters were noticed. However, oxamyl application surpassed them in suppressing nematode population density (68.9%), number of galls (67.6%) and egg-masses (65.8%), respectively, as compared with nematode alone. Meanwhile, among the organic matters tested, pots received poultry manure showed the highest percentage reduction in nematode population density(53.3%), followed by horse manure (51.3%), then periwinkle powder (50.4%), and castor powder (49.4%), as compared with nematode alone. These results demonstrated the potential of such organic matters to protect cotton plant against M. incognita under greenhouse conditions.