Aerobic degradation, photolysis, and mobility of tylosin were investigated in the laboratory. Tylosin A is degraded with a half-life of 200 d in water, while it is stable in the dark. Tylosin C and D are relatively stable except in ultrapure water in the light. Slight increases of tylosin B and formation of two photoreaction products, isotylosin A alcohol (E,Z) and isotylosin A aldol (E,Z), were observed under exposure to light. In soil tylosin A and D has a dissipation half-life of about 1 wk. Sorption and abiotic degradation are the major factors influencing the loss of tylosin in the environment. No biotic degradation was observed at the test concentration of 50 µg/ml or µg/g either in pond water or in an agronomic soil, as determined by comparing dissipation profiles in sterilized and unsterilized conditions. At 7.5 ng/ml, biotransformation may play an important role in degradation of tylosin in water. Tylosin has strong sorption to various soils, and leachbility is dependent on soil properties and manure amendment. Adsorbed tylosin in surface soil might run off to water bodies through soil erosion. In the end, pathways were proposed for tylosin degradation in the environment.