A novel cotton cultivar, designated DP 434 RR, is disclosed. The invention relates to the seeds of cotton cultivar DP 434 RR, to the plants of cotton DP 434 RR and to methods for producing a cotton plant produced by crossing the cultivar DP 434 RR with itself or cotton variety. The invention further relates to hybrid cotton seeds and plants produced by crossing the cultivar DP 434 RR with another cotton cultivar.