Aim. To investigate the TLS-activity of human DNA polymerases β and λ (pols β and λ) using 5-formyluridine (5-foU) containing DNA duplexes which are imitating the intermediates during replication of the leading DNA strand, and to study the influence of replication factors hRPA and hPCNA on this activity. Methods. The EMSA and the methods of enzyme’s kinetics were used. Results. The capability of pols β and λ to catalyze DNA synthesis across 5-foU was investigated and the kinetic characteristics of this process in the presence and in the absence of protein factors hRPA and hPCNA were evaluated. Conclusions. It was shown that: (i) both proteins are able to catalyze TLS on used DNA substrates regardless of the reaction conditions, however, pol λ was more accurate enzyme; (ii) hRPA can stimulate the efficacy of the nonmutagenic TLS catalyzed by pol at the nucleotide incorporation directly opposite of 5-foU, at the same time it doesn’t influence the incorporation efficacy if the damage displaced into the duplex; (iii) hPCNA doesn’t influence the efficacy of TLS catalyzed by both enzymes.