Effect of temperature (5, 10, 15, 18, 21$^{circ}C$) on pre-and post-embryonic development of the sea urchin Strongylocentrotus intermedius was studied. The egg, which measured 122.5 ${mu}{ extrm}{m}$, became globular. At 18$^{circ}C$, it attained 4 celled stage at 3 hours after fertilization, hatched after 15 hours, 4-armed larval stage after 3 days and 8- armed larval stage after 20 days. The relationships between temperature (WT) and time (1, hour) required for each of the selected developmental stages are: Hatching: 1/t=0.0036WT+0.0088 Pyramid: 1/t=0.0014Wl-0.0016 4- armed: 1/t=0.0009WT-0.0020 6- armed: 1/t=0.0004WT-0.0005 8-armed : 1/t=0.0002WT+0.0002 Biological minimum temperature for the egg and larval development is calculated as 1.61$^{circ}C$.