Boutourlini‟s blue monkeys (Cercopithecus mitis boutourlinii) are endemic subspecies of Cercopithecus mitis that found in the north and south western parts of Ethiopia. The study about population estimate, activity pattern and conservation threats of blue monkeys was carried out in Apini and Dikuma forests from October 2018 to June 2019. Data were collected for a total of 80 days in the two forests covering both the wet and dry seasons. Block count technique was applied to count the total population size, and scan sampling method within 15 minutes interval during 5 minutes period was used to collect data for activity patterns, and feeding activity of blue monkeys. On average a total of 71 and 111 individuals were counted in Apini and Dikuma forests, respectively. From the activity time budgets, blue monkeys spent more time for feeding 47.5% and 48.6% by Apini and Dikuma groups, respectively followed by 20.2% moving and 14.1% resting by the Apini group and 18.6% and 13.5% by Dikuma group. They also spent 12.3% and 14.3% of their time for socializing in the Apini and Dikuma groups, respectively. The blue monkeys frequently consumed young leaves (52.8%) and fruits (30.2%) in the Apini and (39.8%) and (42.3%) in the Dikuma. They also feed on mature leaves (6.6%), tree buds (2.5%), stem (2.2%), flowers (3.3%), seeds (1.3%) and animals prey (1.2%) in the Apini, and young leaves (39.8%), mature leaves (8.3%), tree buds (4.6%), stem (0.5%), flowers (1.2%), seeds (1.8%) and animals prey (1.6%) in Dikuma. Out of 14 plant species, Albizia gummifera and Hyppocratea spp. were the most dominant plant species foraged by the study species in both forests. Home range size was 44.4 ha and 78.3 ha for the Apini group, and 51 ha and 56.9 ha for the Dikuma group during the wet and dry seasons, respectively. As, deforestation and agricultural expansion were the major conservation threats for the species, there is a need to design a strategy for minimizing such problems in the area.