Tremella fuciformis, a typical dimorphic fungus, displays two distinct morphological transitions: (i) yeast-pseudohyphae transition; (ii) yeast-hyphae transition. To understand the mechanism of its dimorphism, we initiated a study by investigating how environmental factors affect the yeast-to-pseudohypha transition, including pH value, temperature, carbon source, nitrogen source, cultural time, ethanol and inoculum size. Our studies showed that the optimal conditions for yeast-to-pseudohypha transition were as follows: incubating at 25 to 30°C for 3 to 7 days in media containing glucose as the carbon source, ammonium as the nitrogen source and 10 ml/L ethanol. Below a threshold of inoculum size (10⁵ cells/L), the transition ratio fluctuated markedly, which made us propose that quorum sensing molecules contribute to the dimorphic behavior in T. fuciformis.