Novel 3-(substituted)-2, 4,8,15-tetroxa-3-phosphadispiro[5.2.5]hexadecane-3-oxides (3-12) have been synthesized by cyclization of 1,5-dioxaspiro[5.5]undecande-3,3-dimethanol (1) with various substituted aryl phosphorus dichloridates (2) in dry toluene-THF in the presence of triethylamine at 40-60 °C. Their molecular structures were determined by ir, nmr and mass spectral studies and were screened for antifungal activity against Curvularia lunata and Aspergillus niger, and antibacterial activity on Staphylococcus aureus and Escherichia coli. Most of them possess significant activity.