The present study aimed to investigate the effect of using progesterone- and prostaglandin analogue-based synchronization programs on follicular dynamics and conception rate in subtropical ewes during winter and spring breeding seasons. A total of  80 ewes were assigned into 4 equal groups; Sponge-Spring (SS), Sponge-Winter (SW), PGF₂α-Spring (PS) and PGF₂α-Winter (PW). In PGF₂α-based protocols, 2 injections of natural PGF₂α with10 days apart were used. In progesterone-based protocol, one intravaginal progestagen impregnated sponge inserted for 14 days. The estrus behavior was detected every 4 hrs after the second injection of PGF₂α or the withdrawal of sponge (Day 0) until  the estrus signs were no longer detected using teaser rams. Mating with fertile rams was scheduled every 12 hours during heat. Ultrasonography examinations were started at day 0 and every 12 hrs for 5 days. The results showed that season significantly affected the duration of estrus (P < 0.05) which was longer in winter than spring (SW; 29.6  ± 3.0,  PW; 27.1 ± 1.8 Vs. SS; 21.7 ± 2.0 PS; 16.3 ± 3.0 hrs), while the onset of estrus started at the same times in all groups. On the other hand, the treatment manipulated the patterns of follicular growth. In sponge groups,  the pattern was classified according to the number of ovulatory follicles (single or multiple) while in PGF₂α groups the classification was according to the origin of follicular wave (before or after second PGF₂α treatment). We found that 22% of dominant follicles were ovulated within 12 hours after injection of PGF2α. The study revealed that season and treatment affected the conception rate and litter size. The spring season significantly decreased the conception rate (P<0.05) regardless of the treatment, while sponge increased the litter size (P<0.001) in comparison to PGF₂α. It was concluded that treatment and season had significant effect on the efficacy of estrus synchronization programs in SAIDI ewes. Using progesterone based programs in winter season increased the conception rate and litter size in comparison to PGF₂α programs.