The present invention provides a composition including a polar organic extract of Eurycoma longifolia and a fraction derived from the polar organic extract, said composition comprising of quassinoids, coumarins, their glycosides, analogues and derivatives, which exhibits bioactivity of increasing spermatozoa production and spermatozoa quality in terms of morphology and motility, as well as increasing testosterone synthesis and release from cells of males. The extraction method of E. longifolia plant to produce the polar organic extract, and the subsequent purification to produce the fraction of polar organic extract containing the quassinoids, coumarins, their glycosides, analogues and derivatives, and uses for manufacturing a preparation for infertility treatment are also provided. The fraction of polar organic extract containing the quassinoids, coumarins, their glycosides, analogues and derivatives is formulated for medical applications via several routes of administration.