With 980 nm laser diode (LD) pumping sources, 2.7 µm emission of Er3+-doped tungsten-tellurite (TWL) glasses were investigated. Absorption spectra were measured and an irregularly increased absorption predicted the phenomena of concentration quenching or clustering at 4 mol% Er2O3 concentration. Emission properties of 2.7 µm, 1.5 µm and visible regions were tested to evaluate the energy transfer process of Er3+ ions. With the increment of Er3+ ions, the excited-state absorption (ESA) from Er3+: 4I13/2 level was becoming more apparent and the lifetime of 1.5 µm emission was decreased. At the same time, the up-conversion emissions at green and red regions were decreased. These phenomena gave the evidence of concentration quenching or clustering. Thus, the best concentration of Er3+ ions in this tungsten-tellurite glass was about 3 mol%. Based on its advantages on high solubility of Er3+ ions, strong emission and good thermal stability, tungsten-tellurite glass is a good candidate for mid-infrared laser matrix.