Purpose: This in vitro study aimed to evaluate the influence of the manual manipulation of two composite resins: Filtek™ Z350XT (3M ESPE) and Herculite Précis® (Kerr), with latex gloves contaminated with powder, human saliva and alcohol, on the microhardness values. Material and Methods: Manual manipulation was evaluated using latex gloves with powder, latex gloves without powder, latex gloves without powder with saliva, latex gloves without powder with alcohol, and without hand manipulation or contaminants (control). Each resin was manually manipulated for 10 seconds and photoactivated for 20 seconds with a light intensity of 1000mW/ cm2 using a VALO –Ultradent LED light– cured unit, and then each sample was evaluated on the microhardness Vickers tester Leitz (Wetzlar). The collected data were analyzed using Kruskal –Wallis and Mann – Whitney post-test (p<0.05). Results. Microhardness values showed a significant difference between the evaluated and control groups, showing lower microhardness values in the group of latex glove with powder for Filtek™ Z350XT and the group of latex glove without powder with saliva for Herculite Précis®. Conclusion. The manual manipulation of composite resins decreases their surface microhardness.