Protein-energy malnutrition is one of the major public health problems in developing countries of the world due to prevailing socio-economic problems. This study aimed to observe the effect of formulated complementary blends on biochemical parameters of rats. Extruded complementary blends from maize fortified with cowpea or soybean at a level of 35% and 25% respectively were fed to 4 groups of rats for 28 days. Similarly, 3 other groups of rats were placed on casein, non-protein or rat pellet diet. Biochemical analysis was done on blood samples of the rats. Results from previous studies show the protein content of the formulated diets to range from 15.75% in UMC to 17.24% in MMS. Significantly (p < 0.05) lower WBC, Hb, MCHC, total protein, albumin and globulin values were recorded for the rats fed a non-protein diet (NP). The serum AST level was 75.5, 71.2, 63.2, 51.0, 60.5 and 55.7, respectively, for rats on casein, rat pellet, MMS, UMS, MMC and UMC (list of abbreviations is shown in the appendix) diets. Alkaline phosphatase was significantly (p < 0.05) higher in soybean-based diets while cholesterol was lowest in rats fed the non-protein diet (NP). The value obtained for serum electrolyte concentration in the rats fed NP compared well with rats on other diets but, however, had a significantly (p < 0.05) higher serum sodium value. These results confirm that the experimental diets supported growth, as shown in a previous study, and had no harmful consequence.