Annual bluegrass (Poa annua L.) encroachment into newly established creeping bentgrass (Agrostis stolonifera L.) reduces putting green quality. Previous studies have demonstrated increased annual bluegrass encroachment in stands of creeping bentgrass fertilized with nitrogen (N) and phosphorus (P) compared to stands receiving no or very little N and P additions. However, the effects of N and P on annual bluegrass encroachment into newly established creeping bentgrass putting greens have not been investigated. The objective of this study is to determine how combinations of N and P at varying rates affect annual bluegrass encroachment into a new creeping bentgrass putting green. The study was conducted from 2003-2005 in University Park, PA on a two-year- old USGA specification putting green seeded to ‘Penn A-4' creeping bentgrass. The experiment is a four by four factorial (N rates and P rates) arranged in a randomized complete block design with three replications. Annual bluegrass counts, clipping yields, N and P tissue concentrations, soil Mehlich-P concentrations, and turf color were compared. Increasing rates of N have shown darker turf color, increased clipping yields and increased N tissue concentrations. Increasing P rates have shown increased P tissue concentrations, and increased soil Mehlich-P concentrations, but no affect on clipping yields or turf color.