Metal nanoparticles have found applications in many fields owing to their unique physicochemical characteristics and ease of surface functionalization. Crucial for these applications is the development of environmentally friendly strategies for nanoparticle preparation. Nanoparticles can be prepared using several physical and chemical methods; however, the use of nontoxic and eco-friendly approaches is receiving increasing attention. Plant cell cultures are sustainable sources of bioactive compounds that can act as reducing and stabilizing agents during nanoparticle synthesis. Here, we describe the procedures used to synthesize silver and gold nanoparticles with cultured cells of Catharanthus roseus. The bioreduction of silver ions to nanoparticles with extract of seed-derived callus of C. roseus is evident from UV-Vis spectroscopy results wherein an absorption maxima is observed at 425nm, indicating the formation of elemental silver. Similarly, reaction mixtures containing cell-free suspension culture filtrate of C. roseus and gold III ions turn wine red after 24h incubation because of gold nanoparticle formation. These methods can be easily adapted for use in the preparation of other metal nanoparticles.