The long period cycloid in multiferroic BiFeO3 influences the potential applications of this material and it has been shown that doping (with La and Mn) enlarges the cycloid period. This proposal concerns an investigation of the BiFe1-xCoxO3 crystal and magnetic structure for two compositions, x=0.2 and 0.4. We propose to make high resolution measurements in the temperature range 15K to 700K and using a 200 ms TOF frame to allow a maximum d-spacing of 4.6 Å to be measured on HRPD. The main goal of these measurements is to determine influence of Co doping on crystal and magnetic structure of multiferroic BiFeO3. The crystal structures at x=0.2 and 0.4 will be refined as the material with x=0.4 has a new tetragonal crystal structure (P4mm), whereas x=0.2 retains the space group R3c characteristic for x=0.