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Cosmological measurements suggest that our universe contains a dark energy component. In order to study the dark energy evolution, we constrain a parameterized dark energy equation of state ω(z) = ω0+ω1(z/1+z) using the recent observational datasets: 157 Gold type la supeovae and the newly released 182 Gold type la supeovae by the maximum likelihood method. It is found that the best fit ω(z) crosses -1 in the past and the present best fit value of ω(0)＜-1 obtained from 157 Gold-type la supeovae. The crossing of -1 is not realized and ω0=-1 is not ruled out in 1σ confidence level for the 182 Gold-type la supeovae. It is also found that the range of parameter ω0 is wide even in 1σ confidence level and the best fit ω(z) is sensitive to the prior of Ωm.