The CdS:Pr3+nanomaterial were synthesized by simple chemical precipitation synthesis method. Praseodymium ion was added in CdS:Pr3+ nanomaterial with different concentration 0.1, 0.2 and 0.3 mol % as a dopant. The absorption spectrum of the prepared nanomaterial have been recorded in the UV-Visible region at room temperature. The optical energy band gape of the CdS:Pr3+ nanomaterial were estimated through direct and indirect method from absorption spectra. The optical energy band gap decreases as the concentration of praseodymium ion increases.