The skeletal isomerization of cyclohexene, in a microcatalytic pulse reactor, was investigated by using aluminium orthophosphates (Al/P = 1) as catalysts. An attempt has been made to correlate the isomerization activity with the acid properties of the solids, measured by means of the irreversible adsorption of different organic bases in cyclohexane, at 298 K, using a spectrophotometric method.Apparent rate constants were calculated in terms of the kinetic model of Bassett and Habgood. Selectivity studies led to the conclusion that 1-MCP and 3-MCP were competitive products. Correlation between the kinetic selectivity factor, σ, and the number of strong acid sites has been sought.A possible parallel reaction pathway is proposed, which agrees with both the observed rates and selectivities.