Single mode and multimode tellurite fibres were drawn from preforms of TZN composition (75TeO2 20ZnO 5Na2O) to which 2 mol-% of BaO or La2O3 had been added in the cladding, and their mechanical properties determined. Average bending strengths of 540 to 830 MPa were found after determination of the Young's modulus, which amounted to 46.3 GPa and 46.1 GPa for TZNB and TZNL, respectively. Compared to fluorozirconate fibres drawn previously under nearly the same conditions, average bending strength increased by more than 30 %. On aging in water, the strength of tellurite fibres with TZNL cladding remained unchanged even after 10 days. That of fluoride decreased by more than 50 % within 24 h. Fractographic analysis on fractured tellurite fibres yielded a mirror constant, M, of 1.017 MPa.m1/2. No difference was seen between aged and pristine fibres. By contrast, the mirror constant of fluoride fibre decreased by 10 % on aging. Vickers indentation on TZNL clad glass resulted in a Vickers microhardness, HV, of 3.18 GPa and a fracture toughness, KC, of 0.25 MPa.m1/2. Based on KC and glass structure, an attempt was made to relate fractographic results to the fractal geometry concept as proposed by Mecholsky.