his study was conducted to evaluate changes in productive performance, in terms of milk yield and its composition, of lactating Damascus goats, resulted of feeding three rations. The three respective rations composed of concentrate feed mixture (CFM) + olive trees by-products, the control ration (R1) contained untreated olive tree by-products; (R2) treatedolive trees by-productswith EM1 (product of EMRO Organization in Japan) and (R3)treated olive trees by-products withEl-mofeed. Eighteen lactating Damascus goats (within three seasons of lactation) aged 24 - 30 months, weighed 37.20±0.2 kg and were in 2^nd - 3^rd season of lactation were distributed according to their live body weight and milk production into three similar groups, (6 goats each). The experiment lasted for 120 days after the does weaned their offspring. Milk yield was significantly (P<0.05) higher with groups treated olive trees by-products with EM1 and El-mofeed than untreated ones. Averages of DM, TDN and DCP intakes were the highest with R2, compared with the other tested rations. Feed conversion value expressed as (kg TDN/ kg milk) was practically similar for both R2 and R3 rations being lower than that of the R1 rations. The feed conversion values expressed as (g DCP/ kg milk) recorded the best values being 76.03, 83.95 and 96.98 g/kg milk for R2, R3 and R1, respectively. The results of blood serum parameters showed insignificantly (P>0.05) values of total protein, albumin and globulin, cholesterol, triglyceride, total antioxidant capacity and urea concentrations. It could be concluded that biological treatments (EM1) and chemical treatments (El-mofeed) to rations of lactating Damascus goats improved milk yield, milk composition and feed conversion.