A baseball hitting trainer comprises a supportive cup, an upper pipe, a lower pipe, an upper sleeve, a lower sleeve, an resilient piece connected between the upper sleeve and the lower sleeve, a locking device for locking the upper sleeve with the resilient piece to the lower pipe, a base fixed to the lower sleeve, a weight block, and a fastening ferrule, wherein the lower pipe is allowed to be inserted through the central through hole of the weight block, and the fastening ferrule is fitted around the lower pipe to fasten the weight block onto the lower pipe, whereby the hitting trainer can provide two modes of operation. Under the swing mode, the weight block can be positioned at various heights by adjusting the weight block along the lower pipe to have the hitting trainer swung at various frequencies and speeds, at which a hitter wishes to practice a hitting.