The use of fibres in concrete is one of the methods to increase the resistance of concrete to high temperatures. A wide range of different types of fibres are currently available. However, as part of the global trend to reduce the environmental impact of the construction industry, the use of new types of recycled fibres is also being proposed. In this work, the behaviour of selected fibre types in cement composite mortar at different loading temperatures was investigated. The fibres used were industrially produced polypropylene fibres, recycled fibres from PET bottles and two types of cellulose fibres of which one type is produced by recycling wastepaper. Fibres were added to the cement composites in percentages ranging from 0, 0.3, 0.6, 0.75, 0.9–1.2 %. The properties of the cement composites, such as flexural and compressive strength, were tested at different fibres percentages at laboratory temperatures of 200, 400, 600 and 800 °C. For all types of fibres used, the workability of the fresh mixture was found to be decreased. Comparable strength results to the reference mixture were obtained when recycled polypropylene and cellulose fibres were used. Based on the results obtained, the most effective fibres dosage was determined to be 0.6 %. The most positive tensile flexural and compressive strength results after a thermal loading of 800 °C were obtained with recycled cellulose fibres compared to the reference mixture without fibres. It was evaluated by microscopic observation that the cellulose fibres are present in the composite even at temperatures around 400 °C, while the polymer fibres are completely burnt out. The research confirmed the clear benefits of using recycled fibres instead of conventionally used polymer fibres.