Teff is the most dominant staple cereals in Ethiopia, but yield levels are extremely low (1.2 t/ha) because of declining soil fertility, resulting in widespread national food insecurity. The aim of this study was to explore the effect of potassium (K) fertilization on teff yield and nutrient uptake in Vertisols in the central highlands of Ethiopia. Five levels of K (0, 30, 60, 90, and 120 K 2 O kg/ha) were applied as muirate of potash (KCl) arranged in RCBD with three farm fields as replicates. At crop maturity, a plot of 3 m × 3 m was harvested to measure teff yield and yield components and subsampled for laboratory analysis to determine nutrient uptake. Results showed a highly significant ( p < 0.01) response of teff to K fertilizer application and significant differences among locations. When averaged across locations, the highest mean grain (1,875 kg/ha) and straw yields (6,774 kg/ha) were obtained with the application of 90 and 120 kg K 2 O/ha, respectively. However, the lowest grain (1,576 kg/ha) and straw (5,798 kg/ha) yields were harvested from control plots. This is about a 20% increase over the control. When averaged for all treatments, the highest mean grain (2,641 kg/ha) and straw (7,794 kg/ha) yields were obtained at Moretina Jiru and the lowest grain (1,280 kg/ha) and straw (4,210 kg/ha) yields were obtained at Sululta. Contrary to the popular view that Ethiopian Vertisols are rich in K, there are sites in the central highlands where K deficiency is limiting teff production. In sites where K-soil level was low and rainfall distribution was adequate, the application of K fertilizer along with the government recommended zinc blend fertilizer – NPSZn: 17.7 N + 35.3 P 2 O 5 + 6.5 S + 2.5 Zn – significantly improves nutrient uptake, agronomic efficiency, and teff yields.