[Objectives] To determine the timing of emergence and mating of Piophila casei (Diptera: Piophilidae), and thereby provide a reference for further research on the sex pheromones of this species. [Methods] The emergence and mating behavior of P. casei were investigated under laboratory conditions [(27 ±1)℃, L︰D = 14︰10]. [Results] The peak of adult emergence occurred in the 8^th day of the pupal stage, and peaked before and after the scotophase to the photophase, with females emerging slightly later than males. The behavior of males and females, differed; males engaged in touching, passing, rushing and clasping, whereas females only engaged in touching and clasping. When males encountered other males or mated females, they would chase both of them, and identify them by clasping and touching. Males attempted to displace other males by lifting the end of their abdomen whereas mated females attempted to displace additonal males by swinging their body vigorously. When males encountered virgin females, they quickly jumped onto the female’s back to mate; females could mate just 1 min after emergence but male could not mate until 30 min after emergence. Mating duration was mainly about 10 min. There was competition between males to mate, males encountering a mating pair would jump on their rivals back and bend down its abdomen while trying to reach over it to mate with the female. [Conclusion] Emergence peaked from before, and after, the scotophase to the photophase. P. casei adults were significantly attracted to new puparia, males recognized and pursued females, and the mating urge of males was much stronger than females.