In this article we establish some fixed point (known also as critical point, invariant point) theorems in quasi-metric spaces. Our results unify and further extend in some regards the fixed point theorem proposed by Dancs et al. (1983), the results given by Quy (2010, 2011), the preorder principles established by , and the results obtained by . In addition, we provide examples to illustrate that the improvements of our results are significant.