Background: Although anaesthetic agents are indispensable during a surgical operation, they can cause haemorheological changes resulting in a dynamic change of blood flow. The dissociative general anaesthetic ketamine and the amide-type local anaesthetic lidocaine find clinical and experimental use in a wide application. Nevertheless, their effects on the viscosity of blood plasma and whole blood have not been researched on an individual and combined basis. This research paper aimed to determine the effects of ketamine and lidocaine when used separately and in combination, in the plasma and whole blood viscosity of male Wistar rats. Methodology: A total of thirty-five male Wistar rats were split into five groups (n = 7) which included Control, Lidocaine, Lidocaine with Adrenaline, Ketamine, and Ketamine + Lidocaine. Two days of intraperitoneal administration of treatments took place. The samples of blood were obtained through cardiac puncture. The LOVIS 2000 M/ME Microviscometer measured plasma and whole blood viscosities; by computing the rolling times of a steel ball through a capillary tube, it calculates the dynamic and kinematic viscosities. One way ANOVA was adopted as the statistical analysis method for the study. Results and Discussion: Individually and in combination, ketamine contributed to the variable changes in plasma and whole blood viscosities independently and along with lidocaine. Whereas the concentration of lidocaine (maximally in combination with adrenaline) had a more negligible effect on the level of viscosity, ketamine had no significant effect on the viscosity level. Ketamine combined with lidocaine was involved in altering viscosity which also was in line with the change of red blood cell deformability, as well as aggregability. Conclusion: Lidocaine raises plasma viscosity especially when used with adrenaline, its impact on plasma viscosity is minimal when compared to that of ketamine.