Ecosystem Service value (ESV) is a technique of assigning monetary value to the services and goods of an ecosystem. The rapid change in land-use land cover (LULC) is a major factor for the change in the capacity of Ecosystem Services (ES). Understanding LULC change and its impact on ESV is vital for decision-making processes. We quantify the spatiotemporal variation of ESV of the Kaffa biosphere reserve in association with LULC dynamics, which is part of the Eastern Afromontane biodiversity hotspot areas. Eight LULC types were identified following a supervised classification using a maximum likelihood technique in ArcGIS 10.5. The ES coefficients published by Costanza and others in 2014 were used to estimate the monetary value through the benefit transfer method. Sensitivity analysis was conducted to control the effect of coefficients on the estimated ESV. The results showed declining of ESV from US$ 5818 million to US$ 5536.9 million from 1986 to 2019 and are expected to decline to US$ 5222.8 million in 2049. The change in ESV revealed a total loss of 4.8%. The reasons for the decline in ESV of the biosphere reserve were the conversion of forestland, grassland, and wetland to settlement and agricultural areas. From the land-use types, the contribution of wetland, forest, and agriculture was the most dominant land use in ESV. Genetic resources, climate regulation, water regulation, and recreation were the highest contributors to the total ESV. We conclude that the cause for the decline of ESV is a land-use change that caused ecosystem degradation.