To evaluate the effect of some metabolic mediators such as insulin or/and L-carnitine on milk yield, reproductive performance of premi- (P1) and multi-parous (P2) cows during postpartum (PP), 40 Friesian cows (20 P1 and 20 P2) were divided into 4 similar groups (10 animals in each, 5 P1 and 5 P2). Animals in the 1^st group (T1) were considered as a control, while those in the 2^nd group (T2) were weekly i.m. injected with 40 IU insulin/100 kg LBW. Animals in the 3^rd group (T3) were weekly administrated with oral dose of 1 g L-carnitine (LC)/100 kg LBW, while those in the 4^th group (T4) were administrated with an i.m injection of 40 IU insulin plus oral dose of 1 g LC/100 kg LBW. All treatments were within 7-10 days after calving up to first service. All animals were kept under the same management and feeding system. All cows were milked twice daily by milking machine. Milk yield was weekly recorded and milk composition was monthly determined for 4 month-lactation. Animals in heat 40-45 days postpartum were artificially inseminated and pregnancy diagnosis was carried out 45 d post-service. Blood samples were collected at 0, 1, 2, 3 wk of treatment, estrus and pregnancy for progesterone (P₄) assay in blood serum. Different reproductive measurements were recorded for 4 month-PP. The obtained data showed that average weekly milk yield (AWMY) was higher (P<0.05) in T4 than in T1, but did not differ from that in T2 and T3 only during the 2^nd month of lactation. T2 and T3 insignificantly increased AWMY as compared to T1. Average daily milk yield (ADMY) or total milk yield (TMY) increased (P<0.05) in T2, T3 and T4 by about 13, 14 and 15% as compared toT1, respectively. AWMY, ADMY and TMY were not affected by parity. Milk composition was not affected by treatment at different lactation months. Percentages of protein, solids not fat and total solids in milk only during the 2^nd month of lactation were higher (P<0.05) in P2 than in P1. Average interval from treatment to estrus (ITE) or to conception (ITC) and number of doses required for conception were the shortest inT3. T2 and T4 showed nearly similar values. T3 showed shorter (P<0.05) postpartum first estrus (PPFEI) and service (PPFSI) intervals than T1 (58.9 and 65.2 vs. 86.9 and 95.3 d, respectively). T3 showed high (P<0.05) conception rate (CR, 78%), least number of services per conception (NSC, 1.33), lowest days open (DO, 81.4 d) and the shortest calving interval (CT, 368 d), while T4 showed the highest (P<0.05) CR (90%). ITE, NTC, ITC, PPFEI, PPFSI, DO and CI were lower (P<0.05), while NSC and CR was greater (P<0.05) in P2 than in P1. Serum P4 concentration at 0, 1, 2 and 3 wk of treatment, 1^st estrus, and estrus of conception was not affected by treatment. Only, serum P4 concentration at pregnancy was higher (P<0.05) in T4 than in T2 and T3, but did not differ from that in T1. Serum P4 concentration was higher (P<0.05) in P2 than in P1 only at estrus of conception and pregnancy.In conclusion, administration with an i.m injection of 40 IU insulin plus oral dose of 1 g LC/100 kg LBW during early postpartum period may consider successful treatment for improving milk yield and reproductive performance of lactating Friesian cows (primi- and multi-parous) under the experimental conditions.