Abstract Gas and dust properties in the Chamaeleon molecular cloud complex have been investigated with emission lines from the atomic hydrogen (H i) and ¹²CO molecules, dust optical depth at 353 GHz (τ ₃₅₃), and J-band infrared extinction (A _J ). We have found a scatter correlation between the H i integrated intensity (W _{H i} ) and τ ₃₅₃ in the Chamaeleon region. The scattering has been examined in terms of a possible large optical depth in H i emission (τ _{H i} ) using a total column density (N _H) model based on τ ₃₅₃. A nonlinear relation of τ ₃₅₃ with the ∼1.2 power of A _J has been found in opaque regions (A _J ≳ 0.3 mag), which may indicate a dust evolution effect. If we apply this nonlinear relation to the N _H model (i.e., N _H ∝ τ 353 1 / 1.2 ) allowing arbitrary τ _{H i} , the model curve reproduces well the W _{H i} –τ ₃₅₃ scatter correlation, suggesting optically thick H i (τ _{H i} ∼ 1.3) extended around the molecular clouds. Based on the correlations between the CO integrated intensity and the N _H model, we have derived the CO-to-H₂ conversion factor (X _CO) on ∼1.°5 scales (corresponding to ∼4 pc) and found spatial variations of X _CO ∼ (0.5–3) × 10²⁰ cm⁻² K⁻¹ km⁻¹ s across the cloud complex, possibly depending on the radiation field inside or surrounding the molecular clouds. These gas properties found in the Chamaeleon region are discussed through a comparison with other local molecular cloud complexes.