The present invention relates to serine protease variants, having improved properties compared to the parent protease, in particular variants of a serine protease derived from a strain of Meripilus giganteus belonging to the S53 family. The varinats according to the invention have in particular increased stability, e.g., increased thermo-stability, increased specific activity, and/or increased expression levels, compared to the parent protease. The present invention also relates to polynucleotides encoding the variants; nucleic acid constructs, vectors, and host cells comprising the polynucleotides; and methods of using the variants.