Pressure fluctuations were used for detecting the changes of mean particle size in fluidized beds by two online and accurate monitoring methods (recurrence and cross recurrence analysis (RA and CRA). In the qualitative approach, both methods contain specific structures changing by variation of the states of fluidized bed. In the quantitative approach, the recurrence rate is not suitable to use in detection of changes in particle size due to its high sensitivity to variations of gas velocity; however, determinism and entropy are suitable. Also, determinism of either recurrence plot (RP) or cross recurrence plot (CRP) is not able to identify small changes in particle size (about 10%), but can detect changes on the order of 20% or more. Moreover, entropy of RP is able to detect small changes of particle size in low velocities (up to 0.3 m/s), but entropy of CRP is sensitive to such a change in all velocities considered in this work.