Ceiba pentandra (L.) Gaertn. belongs to the Bombacaceae family, has a pantropical distribution, and in Brazil, it receives the popular name sumaúma and is commonly found within the periodic flooded forests (várzea) of the Amazon Basin. Its wood is intensively exploited for plywood and veneer, and its disappearance is nowaday reduced by plantations. The objective of this study was to determine the effect of temperature on radicle protrusion and normal seedling development. The following constant temperatures were tested on seed germination: 15, 20, 25, 30 and 35°C with a daily photoperiod of 12 hours. The germination is epigeal the first eophyll did not develop under the test conditions, a seedling was therefore considered to be normal, when the expanded cotyledons were in opposite positions. The seeds of sumaúma germinated under a wide range of temperature. Normal seedling development was 29% at 15°C and 51% at 35°C. The best performance was at 30°C, when radicle emission reached 82% and was initiated three days after sowing, with a mean germination time of 5.7 days. Under the same temperature 79% of the seedlings were normal, first counts could be done after 6.8 days but for stabilization of the process 27.8 days were needed. For both germination criterions, a high germination success could only be achieved at the temperature of 30°C and alterations of + 5°C reduced significantly the germination result.