The effect of light intensity on ovarian maturation and spawning of unablated female Penaeus merguiensis was investigated in a 4 week experiment. The experiment had two different light intensity treatments: BRIGHT (1100 lx) and DIM (2 lx). At starting time, there were four groups of broodstock with four different ovarian maturation stages (II, III, IV and V) in each treatment. Results showed that light intensity plays an important role in controlling ovarian maturation of prawns, especially at the later stages (stages III and IV). Bright light showed an inhibitory effect, whereas dim light favoured ovarian maturation and spawning. Ovarian regression occurred in most stage III and stage IV prawns kept under bright light, while prawns at the same stages developed their ovaries further and spawned under dim light. Proportion of spawners (12.5%), mean number of spawns per prawn (0.12) and mean fecundity (87,300) of prawns were significantly lower (P<0.05) in the BRIGHT treatment, compared to the DIM treatment. Under light intensity of 2 lx, 41.7% of prawns spawned, producing 0.5 spawn per prawn on average with a mean fecundity of 117,300. The results also suggest that the sensitivity of broodstock to light increased from stages II to IV of ovarian maturation, while there were some evidence of light adaptation in stage V broodstock. This study confirmed multiple spawning of unablated P. merguiensis for the first time. Rematuration period was short (6-7 days).