The annually increasing global production of tires ranges around 1 billion and the number of waste tires is growing too. A question comes to the fore how to handle the waste to prevent environmental risks. The most advanced recycling facilities can process waste tires by sophisticated methods leading to their further use. One of products is a so-called rubber granulate which enjoys great interest of gardeners who use it instead organic mulch. In relation with this research, phytotoxicity of rubber granulate made from waste tires was studied in laboratory conditions using a test kit (PhytotoxkitTM) for the determination of inhibitory/stimulating effect. The testing was made on the reference soil and tested seeds were the seeds of white mustard (Sinapis alba L). The granulate was applied onto the soil at rates of 5%, 10%, 25%, 50% and 75%. Research results demonstrated the inhibition of Sinapis alba L. seeds already from the rate of 5%, i.e. 6.50%. In the other rates, the inhibition ranged between 26.37% and 62.36%. The granulate is therefore considered phytotoxic and should not be used on the soil.