The newly detected noxious weed (Parthenium hysterophorus L.) is an invasive alien species in Malaysia. The degree of seriousness of the invasion of parthenium weed can be predicted from the condition of weed seed bank in the soil. A study was conducted to investigate the soil seed bank of parthenium weed at different soil depths in five different locations of Ulu Yam Baru, Batang Kali, Selangor, Malaysia. The soil samples were collected from four depths, 0-5 cm, 5-10 cm, 10-15 cm and 15-20 cm; and five sampling areas were chosen, namely a waste disposal site, a vegetable farm, a cattle farm, a stretch of roadside and an undisturbed area of fallow land. The seeds were extracted using sieve shakers at the laboratory of Universiti Malaysia Kelantan, Jeli Campus. On average, 1321 seeds/m² (13.21 million seeds/ha) were found at the depth of 0-5 cm, 218 seeds/m² (2.18 million seeds/ha) at the depth of 5-10 cm and 121 seeds/m² (1.21 million seeds/ha) at the depth of 10-15 cm. No seed was found at the depth of 15-20 cm. The number of seeds varied in different locations as well. The highest number recorded, 1108 seeds/m² (11.08 million/ha), was from the sample taken from the waste disposal site, followed by the vegetable farm, with 514 seeds/m² (5.14 million seeds/ha). The maximum number of weed seeds (3547 seeds/m²) was from the surface layer of the waste disposal site and the total number of seeds varied from 4432-396 seeds/m², and seeds remained within 15 cm soil depth. The collected seeds from the different soil depths showed 70.6% viability in a seed germination test. The total accumulation of 8300 seeds/m² (83.00 million seeds/ha) in soil of 15-cm depth in Batang Kali is a threat to the environment.