This data study concentrates on the past tense marking in the interlanguage (IL) of Chinese speakers of English. Following the assumptions of Hawkins & Lizska, (2003), it is assumed that unlike native speakers of English, Chinese speakers of English have a higher level of optionality within the past tense marking of their grammars. It is claimed that the primary reason for this occurrence is the lack of the functional feature T(ense) [+/-past] in Mandarin Chinese. If a particular functional feature is missing in a learner's L1 grammar, it is thought that it will be absent in one's L2 grammar as well. Three advanced Chinese speakers of English were tested on the past tense marking in their IL production. Both spontaneous oral and reading speech were used for this data analysis.