Transparent crystalline flbers of similar to 25 mm length and similar to 1 mm diameter of KDP (0.3 and 0.4 mol%)doped L-arginine phosphate (LAP) were prepared by laser heated pedestal growth technique. The crystalline fibers were prepared with similar to 5.4 W Of CW CO2 laser power, similar to 7.7 cm/hr sample rodpushing speed and similar to 19.4 cm/hr fiber pulling speed. The crystalline fibers were almost 100% transparent in 250-1200 nm region with cut-off frequency at 220 nm. Powder and single crystal XRD analysis led to the conclusion that KDP doping did not change the crystal structure of LAP. The calculations based on single crystal XRD data produced the structure of the KDP: LAP identical to undoped LAP. This observation is further confirmed by FTIR analysis. The presence of KDP in LAP was confirmed by energy dispersive X-ray analysis (EDX). The shifting and broadening of the photoluminescent emission also indicated KDP doping in LAP. Thermal behavior of crystalline fiber showed significant increase in the decomposing temperature of LAP on doping with KDP so as to make the melt growth of KDP: LAP easy. (C) 2009 Elsevier B.V. All rights reserved.