Whole cycle and successive phases durations of crop are key traits for adaptation to local conditions. They are known as highly genetically controlled and rice breeders used to refer lines and genotypes to short, medium or late materials. However, even expressed in thermal time, these crop and phases durations are also influenced by environment conditions. To test effect of competition levels between plants on rice phenology, a density experiment was carried out in fields in Camargue region, France, with two genotypes on two consecutive years. Results show that leaf appearance rate is affected by densities during the two observed phases of leaf appearance: the rapid one up to beginning of stem elongation and slower one after. They also show that, with increasing plant densities, rice cultivars reduce the number of leaves on the main stem, initiate panicle sooner, and delay flowering date. Analysis shows that relative growth rates during successive phases are highly correlated to observed variations.