FTIR microspectrometry with in situ temperature variation and IR-peak-mapping capability, and POM characterization were used to study the crystal distribution in dual spherulites in poly(heptamethylene terephthalate). By tracing the crystalline IR bands of the alpha-crystal and beta-crystal to get the crystal distribution, the techniques resolve that the ringed and ringless spherulites comprise alpha- and beta-crystals, respectively. In addition, temperature dependent IR analyses on the spots related to the two crystals also reveal the alpha- and beta-crystals melt at 98 and 104 degrees C, respectively. The ringed and ringless spherulites were proven to be correlated with the alpha- and beta-crystal forms, respectively.