The biological synthesis of silver nanoparticles (AgNPs) was conducted using date palm pit aqueous extract. The first visible sign of the synthesis of AgNPs was the change in colour of reaction mixtures from yellowish to reddish brown. The resulting synthesised AgNPs were characterised using UV-visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The UV-visible spectra gave surface plasmon resonance at 428 nm. XRD confirmed that the silver particles formed in our experiments were in the form of nanocrystals. TEM images revealed the formation of AgNPs with spherical shape and sizes in the range between 1-40 nm. DLS showed nanoparticles with an average size of 27 nm. Fourier transform infrared spectroscopy indicated the role of different possible functional groups (carboxyl, amine, aromatic and hydroxyl) in the formation of AgNPs. AgNPs were stable at 28°C in vitro for over a year without any precipitation or decreased production of antimicrobial effect. Then, the antifungal and antibacterial activities of synthesised AgNPs were investigated. The synthesised AgNPs showed significant inhibitory effects on Rhizoctonia solani (AG2_2) cultures, so that the concentration of 25 µg/ml prevented approximately 83% of the mycelium growth of the fungus. Then, the broth macro-dilution method was used for examining antibacterial effect of AgNPs. The minimum inhibitory concentration and minimum bactericide concentration against Klebsiella pneumonia (PCI 602) and Acinetobacter baumannii (ATCC 19606) were recorded as 1.56 and 3.12 µg/ml AgNPs, respectively.