The electronic structures of 9,10-dimethylanthracene (DMA) and its photodimer: di-paraanthracene (DA) have been studied in the gas phase by UV photoelectron spectroscopy and quantum chemical calculations. The comparison of the spectrum of DA with the spectrum of 9,10-dihydroanthracene (DHA) shows that HOMO ionization is shifted towards lower ionization energy in the former. This is the result of through-space orbital interactions between the two DHA subunits in DA. We have estimated the magnitude of through-space (TS) interaction in DA and found that it amounts to 0.85 eV. This is smaller than TS interaction in [2.2]paracyclophane where the value is 0.95 eV.