Fibrous basic magnesium sulfate-containing pellets comprising an olefin polymer and fibrous basic magnesium sulfate in a weight ratio of 80:20 to 20:80 and further comprising a nucleating agent in an amount of 0.3 to 8 weight parts based on 100 weight parts of the olefin polymer and in an amount of 0.2 to 4 weight parts based on 100 weight parts of the fibrous basic magnesium sulfate are favorably employable for producing molded fibrous basic magnesium sulfate-containing propylene polymer products which show high flexural modulus, high flexural strength and high yield strength in tension as well as excellent thermal stability.