Background: Injectable poly-d,l-lactic acid (PDLLA) is a new collagen-stimulating filler containing PDLLA microspheres and carboxymethyl cellulose. It is available as a lyophilized powder that must be reconstituted with a diluent before administration. The aims of this study were to investigate the efficacy of different diluents and a new accelerating "back-and-forth" method. Methods: Six different diluents, sodium bicarbonate, sterile water for injection (SWFI), normal saline, lidocaine, lidocaine with epinephrine (lidocaine + E), and mannitol, were tested. The recommended "vortex" method for preparation of thin suspensions and a new back-and-forth method suitable for both thin and thick suspensions were compared. Gross and microscopic views of the prepared suspensions were examined. Results: Using the vortex method, only mannitol and SWFI are found to be effective reconstitution diluents for injectable PDLLA. Using the back-and-forth method, all six diluents can be used for reconstitution of injectable PDLLA. Moreover, the time needed for reconstitution of injectable PDLLA by this back-and-forth method is very short, regardless of the thickness of the suspension. Conclusions: Clinically, only SWFI can be used for reconstitution of injectable PDLLA by "hand-shaking" or vortex method. To accelerate the reconstitution time especially when using small amount of SWFI, back-and-forth is the method of choice. Besides, when SWFI is not available, other diluents such as normal saline, lidocaine, or lidocaine + E can be used by this novel back-and-forth reconstitution method.