In the thesis light intensity attenuation-based fibre-optic chemical sensors are investigated. The investigation proceeds along two lines: theoretical analyses and design studies. Both intrinsic and extrinsic types of sensors are discussed from both aspects.;The theoretical analyses are concentrated on the construction of theoretical models and numerical calculations, which were previously not well developed but have been attracting a great deal of attention of researchers for some time. Under this topic, fibre-optic evanescent wave absorption sensors and fibre-optic surface plasmon resonance (SPR) sensors are studied as examples of the intrinsic type of sensors, and two-wavelength Beer-Lambert law based fibre-optic sensors as the extrinsic example.;The design studies are concentrated on the design of novel types of sensors which have potentially valuable applications. As the intrinsic type of sensors, novel types of fibre-optic surface plasmon resonance (SPR) chemical sensors are proposed and studied in both point and distributed systems. A fibre-optic sensor for concentration determination of the infusible anaesthetic Propofol is studied in detail as an example of an extrinsic type of sensor.