The influence of temperature on the rate of egg production and embryonic development of Microcotyle sebastis was investigated to determine the precise time of a second treatment. The survival time of the adults of M. sebastis was inversely proportional to temperature. The number of laid eggs per each replicate during the first 24 h was $39.3{pm}4.0$ at $10^{circ}C$, $62.7{pm}14.2$ at $15^{circ}C$, $101.0{pm}5.6$ at $20^{circ}C$ and $89.0{pm}11.0$ at $25^{circ}C$. The time required for egg hatching of M. sebastis was $31.30{pm}4.88$, $17.52{pm}3.24$, $11.59{pm}3.02$ and $10.76{pm}3.10$ days at 10, 15, 20 and $25^{circ}C$, respectively. The regression models of the time required for the beginning and 50% point of hatching according to the different temperatures were as follows; Beginning of hatch: D=58.2000-$4.2067{ imes}Temp+0.0867{ imes}(Temp)^2$ ($Pleq0.01$), 50% of hatch: D=91.3833-$7.5767{ imes}Temp+0.1767{ imes}(Temp)^2$ ($Pleq0.01$).