The reason for the recent study was to inspect the therapeutic efficacy of meloxicam and phenylbutazone alone with their analgesic interaction and their subsequent inhibitory interaction at the level of cyclooxygenase-2 in mice. Meloxicam and phenylbutazone had the analgesic-median effective doses (ED50s) of 15.57 and 119.73 mg/kg, i.p., respectively, given once to mice separately as determined by the up-and-down procedure using a hot plate method. The estimated analgesic ED50s for meloxicam and phenylbutazone combination were at 12.84 and 98.75 mg/kg, i.p., correspondingly when given together at a ratio of 1:1 of their ED50s. The isobolographic analysis reveals that the analgesic interaction between meloxicam and phenylbutazone was antagonistic, as indicated by the interaction index of 1.65. The ELISA technique was used to estimate the cyclooxygenase-2 activity, reflecting that meloxicam or phenylbutazone significantly inhibited the cyclooxygenase-2 activity by 72 and 90%, respectively, compared to the control group. The combination composed of meloxicam and phenylbutazone has a lower limit of inhibition of the cyclooxygenase-2 activity (33%) in comparison to meloxicam or phenylbutazone. Meloxicam and phenylbutazone coadministration were significantly different from the control, meloxicam, and phenylbutazone groups concerning the cyclooxygenase-2 activity in mice. The sum of the data concluded that meloxicam and phenylbutazone have an excellent analgesic efficacy when administered alone. In contrast, the mixture of these two drugs has no benefit because of the antagonistic interaction at cyclooxygenase-2 in mice.