This study aimed to examine the combined effects of urea and calcium hydroxide ensiled oil palm fronds on rumen fermentation and digestibility of Thai native-Anglo Nubian goats. A 4 x 4 Latin square design was used to randomly assign four male crossbred goats (Thai native x Anglo Nubian). The dietary treatments were as follows: ensiled oil palm frond with no additives (EOPF as the control), urea 5\% (50 g/kg fresh matter) (E-UOPF 5\%), calcium hydroxide (Ca(OH)(2)) 5\% (50 g/kg fresh matter) (E-CaOPF 5\%), and combination of urea 2.5\% (25 g/kg fresh matter) with Ca(OH)(2) (25 g/kg fresh matter) (E-UCOPF 2.5\%). The oil palm frond ensiled with different additives did not change the DM intake (p > 0.05). The total TMR intakes range from 69.39 to 77.09 g/kg BW0.75. The goats fed with E-UOPF 5.0\% consumed significantly more CP than the other groups (p < 0.05). The E-UCOPF increased ME intake by 4.8\%, compared with the control treatment (p < 0.05). E-UOPF 5\% and E-UCOPF 2.5\% significantly increased the CP digestibility by 19.7\% and 17.1\%, respectively (p < 0.05). Furthermore, E-CaOPF 5.0\% and E-UCOPF 2.5\% improved the NDF digestibility by about 10.9\% and 9.90\%, respectively (p < 0.05). The urea-containing oil palm frond (E-UOPF 5.0\% and E-UCOPF 2.5\%) had higher blood urea nitrogen (BUN) than the other groups (p < 0.05). The TVFA of goats fed E-UCOPF 2.5\% was approximately 15.8\% higher than that of goats provide EOPF (p < 0.05). The mean concentration of C3 increased by 7.90\% and 11.61\%, respectively, when E-CaOPF 5.0\% and E-UCOPF 2.5\% were provided instead of EOPF (p < 0.05). The total N intake and absorbed were highest (p < 0.05) when goats offered E-UOPF 5.0\% (p < 0.05). The goats fed oil palm frond without additives had the lowest percentage of N-absorption/N intake (p < 0.05). This study clearly shows that the most suitable treatment is E-UCOPF 2.5\%, which enhances DMD, nutrient digestibility, TVFAs, and nitrogen balance and has no negative effects on rumen microbes. This indicates that E-UCOPF 2.5\% may be utilized as an alternate roughage source in TMR diets, accounting for at least 40\% of the OPF. However, several factors still require consideration for urea-Ca(OH)(2) treatments to be successful, including other concentrations of urea, moisture content, duration of pre-treatment, and the metabolizable protein system.