Low Temperature Co-fired Ceramics (LTCC) are functional components which can be utilized as ceramic circuit boards, for instance in mobile phones or as WLAN-, bluetooth-, or radar-antennas. The LTCC-technology provides components with improved thermal, chemical and geometrical stability compared to the widely used PCB (printed circuit board)-technology. Nevertheless, they are often used in critical environments (e.g. temperature, vibrations). Therefore, the mechanical properties must be characterised. LTCC-components are laminates of a glass-matrix with ceramic filler, with an complicate micro-3D network of metal structures. Due to the filled glass-matrix, the metal structures and the matrix can be sintered together at low temperatures (i.e. below 900 °C). The low temperatures allow the use of good electrical conductors like silver, gold or silver-paladium-alloys for the metal structures. The structural integrity of LTCCs is associated with their mechanical strength and resistance to crack propagation. To provide safe and reliable components, the formation and growth of cracks have to be understood. In glass containing materials subcritical crack growth mechanisms (“stress corrosion”) have to be taken into account, where the mechanical strength is affected by the environmental conditions (i.e. temperature and humidity). In this work, the biaxial strength of LTCC specimens (without metallization) is investigated using the ball-on-three-balls test in different environments (water, air, silicon oil, argon) and different temperatures (–40 °C to 125 °C). The experiments unfold a strong environmental impact on the characteristic strength. In inert atmosphere (argon) high strength values can be obtained (i.e. ≈450 MPa), whereas in high humidity environments (e.g. water) under prolonged loading times low strength (220 MPa) are measured. With this work the strong dependence of LTCC mechanical strength on the environment has been shown and quantified. As a result the environment where the component is to operate has to be taken into account in design and production to enhance the component lifetime.