The present study was conducted to investigate the effect of dietary supplementation of organic selenomethionine (SeMet) complex on performance, egg yolk oxidative stability, and immunological responses of laying hens fed diets with different fat sources. A total of 270 Hy-line W-36 Leghorn hens of 47-wk of age were randomly distributed among 5 replicate pens of 9 experimental treatments. Dietary treatments consisted of a 3 × 3 factorial arrangement of treatments with three different supplemental fat (soybean oil, yellow grease, and palm fatty acids powder) and three different levels of organic selenium (0, 0.2, and 0.4 mg/kg of diet as supplied by SeMet complex), that fed during a 77 d feeding trial including 7 days for adaptation period and 70 days as main recording period. Hen-day egg production and egg weights were recorded daily, but all performance parameters were reported as 35 days intervals. The results showed that different fat sources had a significant (P 0.05) effect on egg weight, with the highest weights assigned to soybean oil-fed groups. Dietary supplementation of palm fatty acid powder caused a considerable decrease (P 0.05) in egg weight. In contrast to first 35 d period, dietary SeMet supplementation resulted in a significant (P 0.05) increase in egg weights and incremental Se levels to 0.4 mg/kg increased egg weights. Egg production rate was affected (P 0.05) by both dietary fat source and Se level. During the first 35 d period, egg mass was affected by dietary fat source (P 0.01) and Se level (P 0.05), in part resulted from increases in egg production. Dietary supplementation of 0.2 mg/kg Se improved (P 0.05) egg mass regardless of dietary fat source. During the overall trial period, egg mass was influenced (P 0.05) by Se level × fat source interaction, so that dietary SeMet supplementation was more effective in diets already supplemented by yellow grease. Although feed intake wasn’t affected by experimental treatments during the first 35 d period, however, feed intake significantly (P 0.01) declined in hens fed on palm fatty acids-diets during the second 35 d stage. The best feed conversion ratio (FCR) was assigned to the birds fed on soybean oil diets, followed by yellow grease one; however, utilization of palm fatty acids powder resulted in increase in FCR values. Utilization of palm fatty acids caused decrease (P 0.05) in eggshell thickness. Although Haugh unit and yolk color index weren't influenced by experimental treatments during both sampling periods, dietary SeMet supplementation increased yolk index particularly in eggs laid by hens fed on yellow grease diets. The results of oxidative stability analysis showed that the highest yolk malondialdehyde (MDA) values were assigned to yellow grease-fed groups during the first month of refrigeratoring, while the eggs from birds on palm fatty acids powder had the least MDA values. Also, the highest MDA values were assigned to yellow grease groups during the 2 nd and 3 rd months of refrigeratoring. The antibody titer against Newcastle disease virus was increased (P 0.05) by dietary SeMet supplementation; however, dietary fat source had no effect on antibody production against Newcastle antigen. The present findings indicate that dietary utilization of SeMet in laying diets could improve performance parameters and egg oxidative stability, and these responses depend on dietary fat source.