The impact of plant developmental stage on resistance to rice yellow mottle virus was assessed with a virulent isolate of the virus RYMV. Tests were conducted under controlled conditions at Africa Rice research center. Seed of two rice cultivar were sown at regular intervals in order to produce plant at different age at 35, 49, 63, 77 and 91 days after sowing (DAS) corresponding respectively to the beginning of tillering, active tillering, the end of tillering, panicle initiation and flowering. The inoculum was prepared by grinding 60 g of rice yellow mottle virus infected leaves with 1000 ml of distilled water in a mortar washed with alcohol. The plants were inoculated manually by rubbing the leaves from the leaf base to the tip with fingers moistened with inoculum. Visual leaf chlorosis, chlorophyll (SPAD), virus content and yield reductions due to RYMV were evaluated. Result showed that the two rice cultivars Bouake 189 and CT9153-11-7-1-1 were more susceptible when inoculated at 35 and 49 days after sowing (DAS), attaining up with 99 % and 93% yield loss respectively for the two rice cultivar at 35 DAS. When inoculated at 63 DAS, these cultivar were observed to have developed partial resistance and became total resistance at 91 DAS attaining up 3% yield loss.