We present a discussion of the behavior of π-π scattering lengths under the presence of an external magnetic field, including also finite temperature effects. In this way, we are able to analize the interplay between temperature and strength of the magnetic field. Our analysis is done in the frame of the linear sigma-model, and our calculations are exact within this context. No approximations are introduced for handling the summation over Landau levels and Matsubara frequencies. Although the effects are comparatively small, it is interesting to remark that magnetic field and temperature display opposite effects over the scattering lengths.