Porphyra haitanensis is an economically important marine crop in southern China. A major problem in Porphyra farming is thallus decay in response to high temperature stress. Molecular studies of temperature stress can help to resolve the issue of thallus decay. In this study, to study the molecular mechanism of high temperature tolerance in P. haitanensis, the technology of annealling control primer (ACP) was used to screen the differential expressed genes in gametophytic blades of an F4 high temperature tolerance line Z-61. By the primers combination of dT-RSL and RSL2, one differential expressed gene fragment was cloned. And the full length sequence of this gene fragment was cloned by 5’RACE technology and named as Phrps15a（acceession number JN991055.1）. The Phrps15a gene with a 676bp sequences contains an open reading frame of 390bp encoding a PhRPS15a protein of 130 amino acid residues. The PhRPS15a protein which was assembled by 3 helix, 7 sheet and 8 cycle shared high amino acid sequence identity with RPS15 from other organisms (78~80%), and its molecular formula was C664H1066N188O180S7. Phylogenetic analysis showed that the evolution of PhRPS15a of animal, higher plant, green algae and P.haitanensis has unattached evolutional group, and the PhRPS15a protein of P.haitanensis has closer relation with RPS15a proteins from green alga than ones from other organisms. The results of real-time quantitative PCR indiacted that the expressed level of Phrps15a has high relation with high temperature stress. Under high temperature stress, the expression of Phrps15a gene was down-regulated significantly.