H3.3 is a replication independent histone H3 variant that replace H3 into nucleosomes. It is Incorporated into nucleosomes by histone chaperone Hira and the ATRX/DAXX complex. Loss of all h3.3 genes lead to end of the lineage of the mutant in every studied organism except C. elegans. In this master thesis I demonstrate that loss of all 5 of the h3.3 genes in C. elegans lead to a phenotype. I show that it results in a lower brood size at low temperature stress and that is not cause by embryonic lethality. I also show that H3.3 null worms are more sensitive to heat shock but that pre-adaptation period before the heat shock restore the wild type phenotype. I present evidence that this effect is due to a miss expression of heat shock gene in the H3.3 null mutant. I also study the phenotype of HIRA null mutant. It has a protruding vulva and extreme low brood size. Using EMS screen, I identified a mutant that suppress the over low brood size of HIRA null mutant at 25 °C.