We examined the growth variation with water depth, interval between suspended lines and locality of seedling production of sea squirt. Halocpthia roretzi, measuring approximately $10.1~15.3$ mm in tunic height, was cultured at the farm near Guryongpo, Pohang city from 7 January to 6 December 1998 (333 days). Growth condition depending on culture depth was most favourable at the depth of $10~12$m, It was concluded that nutritional conditions were better at the depth since there was a greater mount of phytoplankton than at any other depth in the water column. Growth condition depending on distance between suspended lines was most favourable at the interval of 2 m and 2.5 m than at the interval of t m and 1.5 m, There was no significance difference in growth variation with locality of seedling. The seasonal variations in growth of tunic height, meat and total weight were correlated with temperature and chlorophyll a, In the depth of $10~12m$ the rate of increase in tunic height was generally greatest in the growth period II ($244{mu}m/day$) and IV ($338{mu}m/day$), lower in the period I ($108{mu}m/day$), and slightly increased during the period III ($185{mu}m/day$). The water column have showed a typical seasonal pattern with temperature ranged between $12.07{sim}24.14^{circ}C$ and over $20^{circ}C$ between July and September.