This study was conducted to identify the effects of caffeine on the lipid and protein components or blood chemistry levels of the serum as well as the total homogenate, mitochondrial and microsomal fraction of the rat(Sprague-Dawley, female) liver. Acute test were conducted to determine those effects. The acute test was conducted by dividing rats into 7 groups according to the time lapsed after a single oral administration of 100mg/kg caffeine(that is control, 2hrs, 4hrs, 8hrs, 24hrs, 48hrs and 72hrs lapsed group). The concentrations of glucose, urea nitrogen, uric acid, creatinine, total protein, albumin, A/G ratio, triglyceride, total cholesterol, HDL-cholesterol, free fatty acid, phospholipid as well as the activities of alanine aminotransferase(ALT), aspartate aminotransferase(AST) and alkaline phosphatase(ALP) were measured in the serum of each experimental groups. The concentrations of the carbonyl group, malondialdehyde(MDA) and the patterns of the SDS-PAGE(Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis) were analyzed to determine the oxidative damages and metabolic changes on the lipid and protein components in the serum, and total homogenate, mitochondrial and microsomal fractions of the rat liver. The results obtained from this study were summarized as follows; 1. The concentrations of serum glucose were significantly higher(p<0.01) between 4(143.0mg/dl) and 8hrs(138.0mg/dl) in comparison to that of the control(101.1mg/dl) after a single oral administration of caffeine(100mg/kg). While on the other, there were no significant differences in the concentrations of urea nitrogen, uric acid, creatinine, total protein, albumin and albumin/globulin(A/G) ratio in comparison to those of the control. 2. The concentrations of total cholesterol and HDL-cholesterol in serum were significantly higher(p<0.01) between 4(77.4mg/dl, total cholesterol) and 8hrs(64.7mg/dl, HDL-cholesterol) in comparison to those of the control(62.8, 46.7mg/dl) after a single oral administration of caffeine(100mg/kg). On the other hand, the concentrations of triglyceride in serum were significantly lower(p<0.01) after 8hrs(38.8mg/dl) in comparison to that of the control(66.5mg/dl). 3. The activities of AST in serum was significantly higher(p<0.05) from 2hrs(149U/L) to 8hrs(178U/L) in comparison to the control(112U/L) after a single oral administration of caffeine(100mg/kg). The activities of ALT in serum were significantly higher(p<0.01) at 4(45.5U/L), 24(49.3U/L), 48(46.8U/L) and 72 hrs(42.3U/L) in comparison to that of the control(39.7U/L) after a single oral administration of caffeine(100mg/kg). On the other hand, there were no significant differences in the activities of ALP in comparison to that of the control. 4. The concentrations of free fatty acid in serum were significantly higher(p<0.01) at 8hrs(65.0mg/dl) in comparison to that of the control(37.6mg/dl) after a single oral administration of caffeine(100mg/kg). However, there were no significant differences in the concentrations of carbonyl group and malondialdehyde within serum, and liver homogenate, mitochondrial and microsomal fractions in comparison to that of the control. 5. The patterns of SDS-PAGE in serum, mitochondrial and microsomal fraction of the liver showed no significant differences.