P-Methoxycinnamic acid (PMCA) was an anti-inflammatory agent owing mechanism of action by inhibiting cyclooxygenase enzyme thus disrupted the conversion of arachidonic acid to prostaglandin. Unfortunately, PMCA had poor solubility in water. This affected the bioavailability of the compound in the blood which giving low efficacy. To improve its solubility, the formation co-crystal of PMCA with caffeine was carried out at a molar ratio 1:1 using the solvent evaporation method. Co-crystal was characterized by several methods, such as Differential Scanning Calorimetry (DSC), Powder X-Ray Diffraction (PXRD), Scanning Electron Microscope (SEM), and also Fourier Transform Infrared (FTIR). According to the thermograms, diffractograms, microphotographs, and IR spectra of APMS-caffeine co-crystal had different physicochemical characteristics compared to its physical mixture and also starting materials. The DSC thermogram showed the melting point of co-crystal was 155.09°C. While diffractogram of co-crystal exhibited some new peaks at 9.4054°, 13.8609°, 15.2124°, 17.8274° and 19.2285° of 2θ value. Furthermore, microphotograph of co-crystal showed a columnar crystal habit. It was the different crystal form from the crystal habit of each starting materials, PMCA and caffeine. The IR spectra displayed some changes of absorption bands in the O-H and C=O function groups of the PMCA which indicates hydrogen bonding with caffeine.