The single and interactive effects of light and temperature, salinity, and urea enrichment on the growth and agar yield and quality of Gracilariopsis bailinae were determined under indoor and outdoor tank conditions. Culture period was 6 weeks. Growth rate reached its peak on the second week in all culture conditions and gradually decreased towards the end of the culture period. Higher growth rates were obtained in seaweed cultured in outdoor (0.27-1.12% day^-1) than in indoor (0.21-0.72% day^-1) tanks; with urea enrichment and lower salinity levels (15-25ppt). A significant interactive effect was demonstrated between and among the environmental parameters on the growth of the seaweed. Highest gel strength (870 g cm^-1) and lowest sulfate content (3.1 µg mg^-1) were obtained at 25ppt, without urea enrichment and in indoor tanks. A significant interactive effect of light intensity and temperature-urea enrichment was ascertained on agar yield; also of light intensity and temperature-salinity on gel strength and sulfate content. Positive and negative correlation was likewise established between agar properties.