We have measured the branching fraction B, longitudinal polarization fraction fL, and CP asymmetry coefficients A and S for B0→ρ+ρ- decays with the Belle detector at the KEKB e+e- collider using 253fb-1 of data. We obtain B=[22.8±3.8(stat)-2.6+2.3(syst)]×10-6, fL=0.941-0.040+0.034(stat)±0.030(syst), A=0.00±0.30(stat) ±0.09(syst), and S=0.08±0.41(stat)±0.09(syst). These values are used to constrain the Cabibbo-Kobayashi-Maskawa phase 2; the solution consistent with the standard model is 2=(88±17)° or 59°< 2<115° at 90% C.L. © 2006 The American Physical Society.