The widespread use of lasers in medicine has raised the awareness about the mutagenic effect of ultraviolet laser radiation. Although it is well known that the major target for UVC (200 - 290 nm) and UVB (290 - 320 nm) wavebands on cells and tissues is nuclear DNA, the information about UVA radiation (320 - 400 nm) is controversial, as far as some researchers present evidence that this waveband should be 1000-fold less cytotoxic and mutagenic than UVC, while others present evidence about its lethality and mutagenicity. In addition the mechanism of cell killing in the UVA range remains unclear. This work presents an extensive study of UVA-laser radiation (355 nm) effects on Chinese hamster ovary cells. The experiments were performed with an Nd:YAG/KD*P laser (third harmonic, 355 nm), operating at the Q-switch mode, 6 nsec pulse duration. Chinese hamster ovary cells (CHO cells) from a frozen cell line, were suspended in McCoy's 5A culture medium, washed with PBS, and after centrifuging at 200 g the pellet irradiated by UVA-laser beam. Cell viability studies were done in a range of fluences from 0 - 75 J/cm2, 5 Hz repetition rate. Direct effects of laser irradiation were evaluated by the Trypan Blue test, and post-effects by the cell survival assay. The degree of cell damage was related to the fluence and it was concluded that increasing fluences of radiation resulted in decrease rate of cell survival. Also, it was noticed that the survival fraction 8 days after irradiation was decreased in relation to the survival fraction just after irradiation. Direct and post-effects are discussed and related with pertinent mechanisms of damage and repair by UVA light.