PURPOSE: To obtain the titled compsn. which has improved thermal stability and gives fluorescent pigmented moldings which have marketability and economical advantages, by adding a specified metal salt to a halogen-contg. resin compsn. contg. a Rhodamine dye.

CONSTITUTION: 0.01W10pts.wt. Rhodamine dye (e.g. Rhodamine B of the formula) is incorporated in a halogen-contg. resin (e.g. polyvinyl chloride). 0.01W2.0pts.wt. alkaline earth metal perchlorate [e.g. anhydrous or hydrous Ba(ClO4)2] is added thereto. Optionally, a polymer contg. a Na or K compd. as thermal stabilizer, butylated p-cresol as antioxidant, natural wax as lubricant and butyl acrylate as processing aid is added thereto. The mixture is kneaded to obtain a halogen- contg. resin compsn. contg. Rhodamine dye.