The early stage development response of Japanese flounder to simultaneous gradual drop in salinity (34, 24, 14 psu) and temperature with different durations (1, 3, 6 h) were investigated to gain better understanding of the decrease in natural stock and its relationship to global weather pattern changes. A series of small-scale laboratory set-up containing six replicates per treatment using plastic microplates were each stocked with 78 fertilized Japanese flounder eggs in gastrula stage and exposed to gradual salinity and temperature drop conditions followed by the recovery to ambient conditions. Two-way ANOVA showed that salinity (S) and exposure time (E) individually or as a combination (S × E) had no effects on hatching success rate, percentage of abnormality, pre-anal length, final total length at 4 days post-hatch (dph) and survival rate at 4 dph. Onset hatching time, newly hatched larvae total length and yolk sac volume showed individual effects but recorded no interaction effects between S and E. Results obtained indicated that the early developmental stages of Japanese flounder were quite resilient to the stressful conditions subjected on them.