Abstract: A study was carried out to determine the effect of salinity on ovarian maturation stages (external morphology and histology characteristics of the ovary) and embryonic development (time of embryonic development and size of egg) of mud spiny lobster, Panulirus polyphagus. For the ovarian maturation stages, there were three treatments; treatment 1 for 20 ppt (E1T1), treatment 2 for 40 ppt (E1T2) and control treatment for 30 ppt (E1C2) and conducted within 100 days. There was no significant difference (p>0.05) between control in 30 ppt at day 1 (E1C1), E1C2, E1T1and E1T2 noted in the Oocyte Size Index (OSI). Mean oocyte diameter and Gonadosomatic Index (GSI) had significantly differences (p<0.05) between E1C1, E1C2, E1T1 and E1T2. For the embryonic development, the berried female was placed in tank with 20 ppt for treatment 1 (E2T1), 30 ppt for control treatment (E2C1) and 40 ppt for treatment 2 (E2T2) and 20-30 eggs were taken for each salinity to observe the embryonic development. Stage 1, 2 and 3 for 20 ppt and stage 1 for 40 ppt cannot be observed the development of embryo. At low salinity of 20 ppt (E2T1), the shortest duration from stage 4 until hatched was about 4 days while at high salinity of 40 ppt (E2T2), the longest duration from stage 4 until hatched was about 8 days. Thus, the low salinity was the shortest time to hatch. The effect on the sizes changes was stronger in the salinities of 30 and 20 ppt than 40 ppt. Therefore, the high salinity was the lowest egg size compared to low and control treatments. In conclusion, the different salinity affected the ovarian maturation stages and embryonic development of P. polyphagus.